feat: remove sign-addon (#2880)

* feat: remove sign-addon
* test(functional): Updated amo fake server and sign command functional test to pass with the submit-addon API

---------

Co-authored-by: Luca Greco <[email protected]>

Author: willdurand

Diff for: .nsprc

@@ -1,9 +1,3 @@
 {
-  "exceptions": [
-    // See: https://github.com/mozilla/web-ext/issues/2678
-    "https://github.com/advisories/GHSA-p8p7-x288-28g6",
-
-    // See: https://github.com/mozilla/web-ext/issues/2678
-    "https://github.com/advisories/GHSA-72xf-g2v4-qvf3"
-  ]
+  "exceptions": []
 }

Diff for: CONTRIBUTING.md

@@ -214,7 +214,7 @@ so as not to disturb any real `addons.mozilla.org` data.
 
   ```
   web-ext sign --api-key user:123 --api-secret abc1234 \
-      --api-url-prefix https://addons-dev.allizom.org/api/v4
+      --amo-base-url https://addons-dev.allizom.org/api/v5/
   ```
 
 - Signed add-ons created with the development API are hard to install into