[rubygems/rubygems] Don't memoize in NameTuple lock_name

The result of this is already memoized and no other NameTuple
methods memoize.

https://github.com/rubygems/rubygems/commit/b7cce0c64a

lib/bundler/rubygems_ext.rb

@@ -361,12 +361,11 @@ module Gem
     end
 
     def lock_name
-      @lock_name ||=
-        if platform == Gem::Platform::RUBY
-          "#{name} (#{version})"
-        else
-          "#{name} (#{version}-#{platform})"
-        end
+      if platform == Gem::Platform::RUBY
+        "#{name} (#{version})"
+      else
+        "#{name} (#{version}-#{platform})"
+      end
     end
   end