Straggler rails version tests are never running for booter and response specs

[chadlwilson]

There are some straggler rails version-specific tests/code that are not currently running. Some may have been accidentally omitted from running on newer rails versions; others may have been logic specific to those rails versions that were not actually needed/wanted on newer versions.

• Dead code? (folder doesn't exist I think, but test is passing anyway with and without rails) https://github.com/jruby/jruby-rack/blob/bbbad305553e796016edb898715121885047924d/src/spec/ruby/jruby/rack/booter_spec.rb#L321
• Body closing https://github.com/jruby/jruby-rack/blob/6f88954ba968c4c660761bc4b7e2388e59f61eed/src/spec/ruby/jruby/rack/response_spec.rb#L389-L396
• Dechunking?
  • may or may not be used/needed now (need to investigate whether JRuby::Rack::Response.dechunk = false is used/needed still). https://github.com/jruby/jruby-rack/blob/6f88954ba968c4c660761bc4b7e2388e59f61eed/src/spec/ruby/jruby/rack/response_spec.rb#L156-L239
• Streaming files https://github.com/jruby/jruby-rack/blob/6f88954ba968c4c660761bc4b7e2388e59f61eed/src/spec/ruby/jruby/rack/response_spec.rb#L377-L387

Would also be good to review and remove the associated code if they were specific to ancient rails versions.