Update JRuby version

This brings us to the latest version that's been shipped, and that
brings Java 11 support.

In the process, we've removed the old .Net support, as this is handled
by Buck right now.

Rakefile

@@ -19,14 +19,10 @@ verbose(false)
 require 'rake-tasks/crazy_fun'
 require 'rake-tasks/crazy_fun/mappings/export'
 require 'rake-tasks/crazy_fun/mappings/folder'
-require 'rake-tasks/crazy_fun/mappings/gcc'
 require 'rake-tasks/crazy_fun/mappings/javascript'
-require 'rake-tasks/crazy_fun/mappings/jruby'
-require 'rake-tasks/crazy_fun/mappings/python'
 require 'rake-tasks/crazy_fun/mappings/rake'
 require 'rake-tasks/crazy_fun/mappings/rename'
 require 'rake-tasks/crazy_fun/mappings/ruby'
-require 'rake-tasks/crazy_fun/mappings/visualstudio'
 
 # The original build rules
 require 'rake-tasks/task-gen'
@@ -72,28 +68,13 @@ crazy_fun = CrazyFun.new
 #
 # If crazy fun doesn't know how to handle a particular output type ("java_library"
 # in the example above) then it will throw an exception, stopping the build
-GccMappings.new.add_all(crazy_fun)
-JRubyMappings.new.add_all(crazy_fun)
-PythonMappings.new.add_all(crazy_fun)
 RakeMappings.new.add_all(crazy_fun)
 RubyMappings.new.add_all(crazy_fun)
-VisualStudioMappings.new.add_all(crazy_fun)
-
-# Allow old crazy fun targets to continue to exist
-
-# Not every platform supports building every binary needed, so we sometimes
-# need to fall back to prebuilt binaries. The prebuilt binaries are stored in
-# a directory structure identical to that used in the "build" folder, but
-# rooted at one of the following locations:
-["cpp/prebuilt"].each do |pre|
-  crazy_fun.prebuilt_roots << pre
-end
 
 # Finally, find every file named "build.desc" in the project, and generate
 # rake tasks from them. These tasks are normal rake tasks, and can be invoked
 # from rake.
 crazy_fun.create_tasks(Dir["common/**/build.desc"])
-crazy_fun.create_tasks(Dir["cpp/**/build.desc"])
 crazy_fun.create_tasks(Dir["rb/**/build.desc"])
 
 # If it looks like a bazel target, build it with bazel