Dont allow remove of protected branch

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

lib/gitlab/git_access.rb

@@ -44,8 +44,12 @@ module Gitlab
     def push_allowed?(user, project, ref, oldrev, newrev, forced_push)
       if user && user_allowed?(user)
         action = if project.protected_branch?(ref)
+                   # we dont allow force push to protected branch
                    if forced_push.to_s == 'true'
                      :force_push_code_to_protected_branches
+                   # and we dont allow remove of protected branch
+                   elsif newrev =~ /0000000/
+                     :remove_protected_branches
                    else
                      :push_code_to_protected_branches
                    end