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.

Author: tglsfdc

src/test/regress/expected/regex.linux.utf8.out

@@ -94,7 +94,7 @@ test: create_table_like alter_generic alter_operator misc async dbsize misc_func
 # rules cannot run concurrently with any test that creates
 # a view or rule in the public schema
 # collate.*.utf8 tests cannot be run in parallel with each other
-test: rules psql psql_crosstab amutils stats_ext collate.linux.utf8 regex.linux.utf8
+test: rules psql psql_crosstab amutils stats_ext collate.linux.utf8
 
 # run by itself so it can run parallel workers
 test: select_parallel