Remove unknown keyword arg from DateTime.parse

[headius]

This snuck in while addding tests for the create_additions
feature. Caught by JRuby when we added the limit option to the
Date/DateTime parsing methods, which causes this to be rejected as
an unknown keyword.

[headius]

We opted to exclude this test in jruby/jruby@a9f3b6b because it started to fail when we added the limit option. JRuby's date library is still partially in Ruby, and adding the limit option there meant it started to reject unknown keywords, like `create_additions.

This was not found by CRuby because the option processing in CRuby's date library does not reject unknown keywords.