Fix duplicated branch creation/deletion Web hooks/service notifications when using Web UI

Similar to 423d2d62, except duplicates occurred only if a Web service (e.g. Slack) were
configured.

When deleting a branch, this is what was happening:

    1. DeleteBranchService calls execute_hooks and execute_services
    2. The call to repository.rm_branch triggers the GitHooksService.
    3. This, in turn, calls GitPushService and then calls the same hooks/services again.

5145706c now makes it no longer necessary for DeleteBranchService and CreateBranchService to execute
the branch hooks/services. Note that tags behave differently in GitTagPushService and GitPushService
is not called.

Closes #10330

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.5.0 (unreleased)
   - Cache various Repository methods to improve performance (Yorick Peterse)
+  - Fix duplicated branch creation/deletion Web hooks/service notifications when using Web UI (Stan Hu)
   - Ensure rake tasks that don't need a DB connection can be run without one
   - Update New Relic gem to 3.14.1.311 (Stan Hu)
   - Add "visibility" flag to GET /projects api endpoint

app/services/create_branch_service.rb

@@ -29,11 +29,7 @@ class CreateBranchService < BaseService
     end
 
     if new_branch
-      push_data = build_push_data(project, current_user, new_branch)
-
-      project.execute_hooks(push_data.dup, :push_hooks)
-      project.execute_services(push_data.dup, :push_hooks)
-
+      # GitPushService handles execution of services and hooks for branch pushes
       success(new_branch)
     else
       error('Invalid reference name')

app/services/delete_branch_service.rb

@@ -25,11 +25,7 @@ class DeleteBranchService < BaseService
     end
 
     if repository.rm_branch(current_user, branch_name)
-      push_data = build_push_data(branch)
-
-      project.execute_hooks(push_data.dup, :push_hooks)
-      project.execute_services(push_data.dup, :push_hooks)
-
+      # GitPushService handles execution of services and hooks for branch pushes
       success('Branch was removed')
     else
       error('Failed to remove branch')