Ruby

[ruby/irb] Clear all context usages in RubyLex
(https://github.com/ruby/irb/pull/684)

After this change, RubyLex will not interact with Context directly
in any way. This decoupling has a few benefits:

• It makes RubyLex easier to test as it no longer has a dependency on
  Context. We can see this from the removal of build_context from
  test_ruby_lex.rb.
• It will make RubyLex easier to understand as it will not be affected
  by state changes in Context objects.
• It allows RubyLex to be used in places where Context is not available.

https://github.com/ruby/irb/commit/d5b262a076