Tests: Remove a workaround for a Firefox XML parsing issue
Tests: Remove a workaround for a Firefox XML parsing issue

Firefox 96-100 used to report the column number smaller by 2 than it should
in the `parsererror` element generated for invalid XML documents. Since that
version range is unsupported now and it includes no ESR versions, the workaround
can now be dropped.

Closes gh-5109
Ref gh-5018
jquery/jquery,jquery/jquery,jquery/jquery