src: remove GTEST_DONT_DEFINE_ASSERT_EQ in util.h

As indicated by the FIXME comment, this macro guard is no longer needed.

PR-URL: https://github.com/nodejs/node/pull/12638


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>