tests: remove last uses of GIT_TEST_GETTEXT_POISON=false

Follow-up my 73c01d25fe (tests: remove uses of
GIT_TEST_GETTEXT_POISON=false, 2021-01-20) by removing the last uses
of GIT_TEST_GETTEXT_POISON=*.

These assignments were part of branch that was in-flight at the time
of the gettext poison removal. See 466f94ec45 (Merge branch
'ab/detox-gettext-tests', 2021-02-10) and c7d6d419b0 (Merge branch
'ab/mktag', 2021-01-25) for the merging of the two branches.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3800-mktag.sh

@@ -13,13 +13,11 @@ test_description='git mktag: tag object verify test'
 
 check_verify_failure () {
 	test_expect_success "$1" "
-		test_must_fail env GIT_TEST_GETTEXT_POISON=false \
-			git mktag <tag.sig 2>message &&
+		test_must_fail git mktag <tag.sig 2>message &&
 		grep '$2' message &&
 		if test '$3' != '--no-strict'
 		then
-			test_must_fail env GIT_TEST_GETTEXT_POISON=false \
-				git mktag --no-strict <tag.sig 2>message.no-strict &&
+			test_must_fail git mktag --no-strict <tag.sig 2>message.no-strict &&xb
 			grep '$2' message.no-strict
 		fi
 	"
@@ -443,11 +441,9 @@ test_expect_success 'invalid header entry config & fsck' '
 	git -c fsck.extraHeaderEntry=ignore mktag --no-strict <tag.sig &&
 
 	git fsck &&
-	env GIT_TEST_GETTEXT_POISON=false \
-		git -c fsck.extraHeaderEntry=warn fsck 2>err &&
+	git -c fsck.extraHeaderEntry=warn fsck 2>err &&
 	grep "warning .*extraHeaderEntry:" err &&
-	test_must_fail env GIT_TEST_GETTEXT_POISON=false \
-		git -c fsck.extraHeaderEntry=error 2>err fsck &&
+	test_must_fail git -c fsck.extraHeaderEntry=error 2>err fsck &&
 	grep "error .* extraHeaderEntry:" err
 '