Allow destroying protected branch access levels from the `update` action.

- Using the `allow_destroy` option for `accepts_nested_attributes_for`

app/controllers/projects/protected_branches_controller.rb

@@ -60,8 +60,8 @@ class Projects::ProtectedBranchesController < Projects::ApplicationController
 
   def protected_branch_params
     params.require(:protected_branch).permit(:name,
-                                             merge_access_levels_attributes: [:access_level, :id, :user_id],
-                                             push_access_levels_attributes: [:access_level, :id, :user_id])
+                                             merge_access_levels_attributes: [:access_level, :id, :user_id, :_destroy],
+                                             push_access_levels_attributes: [:access_level, :id, :user_id, :_destroy])
   end
 
   def load_protected_branches

app/models/protected_branch.rb

@@ -11,8 +11,8 @@ class ProtectedBranch < ActiveRecord::Base
   validates_length_of :merge_access_levels, minimum: 0
   validates_length_of :push_access_levels, minimum: 0
 
-  accepts_nested_attributes_for :push_access_levels
-  accepts_nested_attributes_for :merge_access_levels
+  accepts_nested_attributes_for :push_access_levels, allow_destroy: true
+  accepts_nested_attributes_for :merge_access_levels, allow_destroy: true
 
   # Returns all merge access levels (for protected branches in scope) that grant merge
   # access to the given user.