[Upgrade] Remove migratable_vms from iuo files (#3307)

##### Short description:
Since this PR merged, virt team upgrade tests fails because
migratable_vms fixture include non-migratable network vms.
The current implementation relies on execution order which is wrong.
Restoring to the previous state.
##### More details:

##### What this PR does / why we need it:
Until https://issues.redhat.com/browse/CNV-75357 will happen & merge,
4.20 & 4.21 upgrade tests fails.
It may take few weeks.
##### Which issue(s) this PR fixes:

##### Special notes for reviewer:

##### jira-ticket:
https://issues.redhat.com/browse/CNV-75793

Signed-off-by: Harel Meir <hmeir@redhat.com>

Author: hmeir

tests/install_upgrade_operators/product_upgrade/test_eus_upgrade.py

@@ -20,7 +20,6 @@ def test_eus_upgrade_process(
         self,
         admin_client,
         hco_namespace,
-        migratable_vms,
         eus_target_cnv_version,
         eus_cnv_upgrade_path,
         eus_paused_worker_mcp,

tests/install_upgrade_operators/product_upgrade/test_upgrade.py

@@ -50,7 +50,6 @@ def test_cnv_upgrade_process(
         self,
         admin_client,
         hco_namespace,
-        migratable_vms,
         cnv_target_version,
         cnv_upgrade_stream,
         fired_alerts_before_upgrade,
@@ -92,7 +91,6 @@ def test_production_source_cnv_upgrade_process(
         self,
         admin_client,
         hco_namespace,
-        migratable_vms,
         cnv_target_version,
         cnv_upgrade_stream,
         fired_alerts_before_upgrade,