revert(merge-requests): remove server-derived userActions from responses

This reverts merge commit 86b44cd (PR #8039, UT-4120).

GET /v2/storage/merge-request times out (30s max execution time) in
projects with many merge requests because the userActions gates issue
uncached lookups per list item; the failure blocks the production build.
The route-guard-reflection design also needs a rethink, so instead of
patching we revert and will redesign (role policy in the domain, likely
voter-centric) before reintroducing the field.

The field never reached production - both builds containing it failed
on this exact timeout.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: martinsifra

apiary.apib

@@ -10782,7 +10782,6 @@ other buckets (production buckets or buckets belongs the other development branc
                   "status": null
             }
             ],
-            "userActions": ["edit"],
             "createdAt": "2023-06-15T10:20:58+0200"
             }
 
@@ -10843,7 +10842,6 @@ List all merge requests available in the project defined by token.
                       "status": null
                 }
                 ],
-                "userActions": ["approve", "reject"],
                 "createdAt": "2023-06-15T10:20:58+0200"
                 }
             ]
@@ -10926,7 +10924,6 @@ Detail of Merge request also contains `content` of changed objects.
                   "status": null
             }
             ],
-            "userActions": ["approve", "reject"],
             "createdAt": "2023-06-15T10:20:58+0200"
             }
 
@@ -10996,7 +10993,6 @@ Detail of Merge request also contains `content` of changed objects.
                   "status": null
             }
             ],
-            "userActions": ["edit"],
             "createdAt": "2023-06-15T10:20:58+0200"
             }
 
@@ -11070,7 +11066,6 @@ Will move Merge request state `development` -> `in_review`. If branch has an ope
                   "status": null
             }
             ],
-            "userActions": ["approve", "reject"],
             "createdAt": "2023-06-15T10:20:58+0200"
             }
 
@@ -11151,7 +11146,6 @@ Each project has defined required number of approvals. If the last approval arri
                   "status": null
             }
             ],
-            "userActions": ["approve", "reject"],
             "createdAt": "2023-06-15T10:20:58+0200"
             }
 
@@ -11309,7 +11303,6 @@ Requesting changes will remove all approvals and move the Merge request to `deve
                   "status": null
             }
             ],
-            "userActions": ["approve", "reject"],
             "createdAt": "2023-06-15T10:20:58+0200"
             }