Revert "Rename solr_request_handler config variable to qt"

Start trying to remove qt= approach.

This reverts commit 467364a9fecc9a736b4e0caa821ec22238f19bcb.

Conflicts:
	lib/blacklight/solr_helper.rb
	test_support/spec/controllers/catalog_controller_spec.rb
Remove solr_path and qt handling.