Revert "Merge branch 'osw-updates-merge-status-on-api-actions' into 'master'"

This reverts commit 9f5390d8, reversing
changes made to c28ffa1d.

changelogs/unreleased/osw-updates-merge-status-on-api-actions.yml

----
-title: Return more consistent values for merge_status on MR APIs
-merge_request:
-author:
-type: fixed

lib/api/entities.rb

@@ -575,16 +575,7 @@ module API
       expose :work_in_progress?, as: :work_in_progress
       expose :milestone, using: Entities::Milestone
       expose :merge_when_pipeline_succeeds
-
-      # Ideally we should deprecate `MergeRequest#merge_status` exposure and
-      # use `MergeRequest#mergeable?` instead (boolean).
-      # See https://gitlab.com/gitlab-org/gitlab-ce/issues/42344 for more
-      # information.
-      expose :merge_status do |merge_request|
-        # In order to avoid having a breaking change for users, we keep returning the
-        # expected values from MergeRequest#merge_status state machine.
-        merge_request.mergeable? ? 'can_be_merged' : 'cannot_be_merged'
-      end
+      expose :merge_status
       expose :diff_head_sha, as: :sha
       expose :merge_commit_sha
       expose :user_notes_count