fix(docs): remove untested rollback procedure

SM does not support rollback procedure because of the reasons
mentioned in #3484. Because of that, we shouldn't describe it
in our docs.

Refs #3484

Author: Michal-Leszczynski

docs/source/upgrade/index.rst

@@ -286,181 +286,3 @@ Check that cluster is up:
     sctool status -c <cluster>
 
 All running nodes should be up.
-
-Rollback Procedure
-==================
-
-.. note:: Rolling back is not recommended because updated versions contains bug fixes and performance optimizations so you will be going back to a lesser version. This should be only used as a last resort.
-
-Rollback procedure contains the same steps as upgrade but with downgrading the components to older version:
-
-- Stop all ScyllaDB Manager tasks (or wait for them to finish)
-- Stop the ScyllaDB Manager Server
-- Stop the ScyllaDB Manager Agent on all nodes
-- Downgrade the ScyllaDB Manager Server and Client
-- Downgrade the ScyllaDB Manager Agent on all nodes
-- Bring back old configuration (if there was conflict)
-- Start the ScyllaDB Manager Agent on all nodes
-- Start the ScyllaDB Manager Server
-- Validate status of the cluster
-
-Rollback steps
-==============
-
-Stop all ScyllaDB Manager tasks (or wait for them to finish)
-------------------------------------------------------------
-
-**On the Manager Server** check current status of the manager tasks:
-
-.. code:: sh
-
-    sctool tasks -c <cluster>
-
-None of the listed tasks should have status in RUNNING.
-
-Stop the ScyllaDB Manager Server 
---------------------------------
-
-**On the Manager Server** instruct Systemd to stop the server process:
-
-.. code:: sh
-
-    sudo systemctl stop scylla-manager
-
-Ensure that it is stopped with:
-
-.. code:: sh
-
-    sudo systemctl status scylla-manager
-
-It should have a status of *“Active: inactive (dead)”*.
-
-Stop the ScyllaDB Manager Agent on all nodes
---------------------------------------------
-
-**On each ScyllaDB node** in the cluster run:
-
-.. code:: sh
-
-    sudo systemctl stop scylla-manager-agent
-
-Ensure that it is stopped with:
-
-.. code:: sh
-
-    sudo systemctl status scylla-manager-agent
-
-It should have a status of *“Active: inactive (dead)”*.
-
-Downgrade the ScyllaDB Manager Server and Client 
-------------------------------------------------
-
-**On the Manager Server** instruct package manager to downgrade server and the client:
-
-CentOS, Red Hat:
-
-.. code:: sh
-
-    sudo yum downgrade scylla-manager-server-3.x* scylla-manager-client-3.x* -y
-
-Debian, Ubuntu:
-
-.. code:: sh
-
-    sudo apt-get install scylla-manager-server=3.x scylla-manager-client=3.x -y
-
-Downgrade the ScyllaDB Manager Agent on all nodes
--------------------------------------------------
-
-**On each ScyllaDB node** instruct package manager to downgrade the agent:
-
-CentOS, Red Hat:
-
-.. code:: sh
-
-    sudo yum downgrade scylla-manager-agent-3.x* -y
-
-Debian, Ubuntu:
-
-.. code:: sh
-
-    sudo apt-get install scylla-manager-agent=3.x -y
-
-Revert to the old configuration
--------------------------------
-
-If you followed instructions from the Upgrade Steps section and you had configuration conflict when upgrading, then listing the configuration directory should give you both new and old configuration:
-
-.. code:: sh
-
-    /etc/scylla-manager/scylla-manager.yaml # New version that you want to disable
-    /etc/scylla-manager/scylla-manager.yaml.old # Previous version that you want to rollback
-
-To restore the old configuration:
-
-.. code:: sh
-
-    cd /etc/scylla-manager/
-    mv scylla-manager.yaml scylla-manager.yaml.new
-    mv scylla-manager.yaml.old scylla-manager.yaml
-
-The procedure is the same for the ScyllaDB Manager Agent (on all nodes):
-
-.. code:: sh
-
-    cd /etc/scylla-manager-agent/
-    mv scylla-manager-agent.yaml scylla-manager-agent.yaml.new
-    mv scylla-manager-agent.yaml.old scylla-manager-agent.yaml
-
-Start the ScyllaDB Manager Agent on all nodes
----------------------------------------------
-
-On all nodes instruct Systemd to start the agent process:
-
-.. code:: sh
-
-    sudo systemctl start scylla-manager-agent
-
-Ensure that it is running with:
-
-.. code:: sh
-
-    sudo systemctl status scylla-manager-agent
-
-It should have a status of *“Active: active (running)”*.
-
-Start the ScyllaDB Manager Server
----------------------------------
-
-**On the Manager Server** instruct Systemd to start the server process:
-
-.. code:: sh
-
-    sudo systemctl stop scylla-manager
-
-Ensure that it is stopped with:
-
-.. code:: sh
-
-    sudo systemctl status scylla-manager
-
-It should have a status of *“Active: active (running)”*.
-
-Validate status of the cluster
-------------------------------
-
-**On the Manager Server** check the version of the client and the server:
-
-.. code:: sh
-
-    sctool version
-    Client version: 3.x
-    Server version: 3.x
-
-Check that cluster is up:
-
-.. code:: sh
-
-    sctool status -c <cluster>
-
-All running nodes should be up.