Move FindLicense RPC to OPT OUT status

Acceptance testing was successful in
https://gitlab.com/gitlab-org/gitaly/issues/1058. So this is moved to
OPT OUT.

Part of https://gitlab.com/gitlab-org/gitaly/issues/1026

changelogs/unreleased/zj-find-license-opt-out.yml

+---
+title: Detect repository license on Gitaly by default
+merge_request:
+author:
+type: performance

lib/gitlab/git/repository.rb

@@ -1036,7 +1036,8 @@ module Gitlab
       end
 
       def license_short_name
-        gitaly_migrate(:license_short_name) do |is_enabled|
+        gitaly_migrate(:license_short_name,
+                       status: Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |is_enabled|
           if is_enabled
             gitaly_repository_client.license_short_name
           else