Removed return from reserved project migration

This return is redundant as the query now uses "WHERE EXISTS (...)" to
filter out projects without a namespace.

db/post_migrate/20161221153951_rename_reserved_project_names.rb

@@ -112,8 +112,6 @@ class RenameReservedProjectNames < ActiveRecord::Migration
 
   def rename_projects(projects)
     projects.each do |project|
-      next unless project.namespace
-
       id = project.id
       path_was = project.path
       namespace_path = project.namespace.path