pgsql: On second thought, remove regex.linux.utf8 regression test altog

On second thought, remove regex.linux.utf8 regression test altogether.

The code-coverage report says that this test doesn't increase
coverage by one single line, which I now realize is because
I made src/test/modules/test_regex/sql/test_regex_utf8.sql
to cover all the code that this would. So really it's pointless
and we should just drop it.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/987db509ed35ad287c50a7eac381535830f03a29

Modified Files
--------------
src/test/regress/expected/regex.linux.utf8.out | 171 -----------------------
src/test/regress/expected/regex.linux.utf8_1.out | 11 --
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/regex.linux.utf8.sql | 54 -------
4 files changed, 1 insertion(+), 237 deletions(-)