[rubygems/rubygems] Remove unused file

No longer used since
b7f6270b9e.

https://github.com/rubygems/rubygems/commit/76803894a0

test/rubygems/bogussources.rb

@@ -1,9 +0,0 @@
-# frozen_string_literal: true
-#--
-# Copyright 2006 by Chad Fowler, Rich Kilmer, Jim Weirich and others.
-# All rights reserved.
-# See LICENSE.txt for permissions.
-#++
-
-require 'rubygems'
-Gem.use_paths("test/mock/gems")