Do not call 'gem "did_you_mean"' for now

This will slow down the time that the +require+ method takes to load DYM,
but this has caused a build failure in a certain situation:

  https://ci.appveyor.com/project/ruby/ruby/builds/29214253/job/r9u9c8p95tnlftt3#L24965

which is reported as a separate bug:

  https://bugs.ruby-lang.org/issues/16382?next_issue_id=16381

For now this commit should fix the builds, but we should come back and
add back the 'gem' call.

gem_prelude.rb

@@ -1,8 +1,2 @@
-if defined?(Gem)
-  require 'rubygems.rb'
-  begin
-    gem 'did_you_mean'
-    require 'did_you_mean'
-  rescue Gem::LoadError, LoadError
-  end if defined?(DidYouMean)
-end
+require 'rubygems.rb' if defined?(Gem)
+require 'did_you_mean' if defined?(DidYouMean)