t7415: remove out-dated comment about translation

Since GETTEXT_POISON does not exist anymore, there is no point warning
people about whether we should use test_i18ngrep. This is doubly
confusing because the comment was describing why it was OK to use grep,
but it got caught up in the mass conversion of 674ba34 (fsck: mark
strings for translation, 2018-11-10).

Note there are other uses of test_i18ngrep in this script which are now
obsolete; I'll save those for a mass-cleanup. My goal here was just to
fix the confusing comment in code I'm about to refactor.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7415-submodule-names.sh

@@ -151,10 +151,9 @@ test_expect_success 'fsck detects symlinked .gitmodules file' '
 		} | git mktree &&
 
 		# Check not only that we fail, but that it is due to the
-		# symlink detector; this grep string comes from the config
-		# variable name and will not be translated.
+		# symlink detector
 		test_must_fail git fsck 2>output &&
-		test_i18ngrep gitmodulesSymlink output
+		grep gitmodulesSymlink output
 	)
 '