patch 9.1.0757: tests: messages files contains ANSI escape sequences

Problem:  tests: messages files contains ANSI escape sequences
Solution: filter those out in runtests.vim

Also, since we are setting $LC_ALL, we don't need to set $LANG and
$LANGUAGE since those are overridden by $LC_ALL anyhow.

closes: #15788

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index 7a4c4c4..b6e8c80 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -12,7 +12,7 @@
 # Comment out this line to see the verbose output of tests.
 #
 # Catches SwapExists to avoid hanging at the ATTENTION prompt.
-REDIR_TEST_TO_NULL = --cmd 'au SwapExists * let v:swapchoice = "e"' | LC_ALL=C LANG=C LANGUAGE=C awk '/Executing Test_/{match($$0, "([0-9][0-9]:[0-9][0-9] *)?Executing Test_[^\\)]*\\)"); print substr($$0, RSTART, RLENGTH) "\r"; fflush()}'
+REDIR_TEST_TO_NULL = --cmd 'au SwapExists * let v:swapchoice = "e"' | LC_ALL=C awk '/Executing Test_/{match($$0, "([0-9][0-9]:[0-9][0-9] *)?Executing Test_[^\\)]*\\)"); print substr($$0, RSTART, RLENGTH) "\r"; fflush()}'
 
 # Uncomment this line to use valgrind for memory leaks and extra warnings.
 #   The output goes into a file "valgrind.testN"