t: refactor tests depending on Perl substitution operator

We have a bunch of tests that use Perl to perform substitution via the
"s/" operator. These usecases can be trivially replaced with sed(1) and
tr(1).

Refactor the tests accordingly so that we can drop a couple of
PERL_TEST_HELPERS prerequisites.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4029-diff-trailing-space.sh

@@ -18,7 +18,7 @@ index 5f6a263..8cb8bae 100644
 EOF
 exit 1
 
-test_expect_success PERL_TEST_HELPERS "$test_description" '
+test_expect_success "$test_description" '
 	printf "\nx\n" > f &&
 	before=$(git hash-object f) &&
 	before=$(git rev-parse --short $before) &&
@@ -31,7 +31,8 @@ test_expect_success PERL_TEST_HELPERS "$test_description" '
 	git config --bool diff.suppressBlankEmpty true &&
 	git diff f > actual &&
 	test_cmp exp actual &&
-	perl -i.bak -p -e "s/^\$/ /" exp &&
+	sed "s/^\$/ /" exp >exp.munged &&
+	mv exp.munged exp &&
 	git config --bool diff.suppressBlankEmpty false &&
 	git diff f > actual &&
 	test_cmp exp actual &&