[rubygems/rubygems] Removed the related code for minitest-bisect

https://github.com/rubygems/rubygems/commit/83ebdec27a

lib/rubygems/test_case.rb

@@ -32,15 +32,6 @@ else
   require 'bundler'
 end
 
-# Enable server plugin needed for bisection
-if ENV["RG_BISECT_SERVER_PLUGIN"]
-  require ENV["RG_BISECT_SERVER_PLUGIN"]
-
-  Minitest.extensions << "server"
-end
-
-ENV["MT_NO_PLUGINS"] = "true"
-
 require 'test/unit'
 
 ENV["JARS_SKIP"] = "true" if Gem.java_platform? # avoid unnecessary and noisy `jar-dependencies` post install hook