t5316: refactor `max_chain()` to not depend on Perl

The `max_chain()` helper function is used to extract the maximum delta
chain of a packfile as printed by git-index-pack(1). The script uses
Perl to extract that data, but it can be trivially refactored to use
awk(1) instead.

Refactor the helper 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/t5316-pack-delta-depth.sh

@@ -76,18 +76,18 @@ test_expect_success 'create series of packs' '
 
 max_chain() {
 	git index-pack --verify-stat-only "$1" >output &&
-	perl -lne '
-	  BEGIN { $len = 0 }
-	  /chain length = (\d+)/ and $len = $1;
-	  END { print $len }
-	' output
+	awk '
+		BEGIN { len=0 }
+		/chain length = [0-9]+:/{ len=$4 }
+		END { print len }
+	' <output | tr -d ':'
 }
 
 # Note that this whole setup is pretty reliant on the current
 # packing heuristics. We double-check that our test case
 # actually produces a long chain. If it doesn't, it should be
 # adjusted (or scrapped if the heuristics have become too unreliable)
-test_expect_success PERL_TEST_HELPERS 'packing produces a long delta' '
+test_expect_success 'packing produces a long delta' '
 	# Use --window=0 to make sure we are seeing reused deltas,
 	# not computing a new long chain.
 	pack=$(git pack-objects --all --window=0 </dev/null pack) &&
@@ -96,21 +96,21 @@ test_expect_success PERL_TEST_HELPERS 'packing produces a long delta' '
 	test_cmp expect actual
 '
 
-test_expect_success PERL_TEST_HELPERS '--depth limits depth' '
+test_expect_success '--depth limits depth' '
 	pack=$(git pack-objects --all --depth=5 </dev/null pack) &&
 	echo 5 >expect &&
 	max_chain pack-$pack.pack >actual &&
 	test_cmp expect actual
 '
 
-test_expect_success PERL_TEST_HELPERS '--depth=0 disables deltas' '
+test_expect_success '--depth=0 disables deltas' '
 	pack=$(git pack-objects --all --depth=0 </dev/null pack) &&
 	echo 0 >expect &&
 	max_chain pack-$pack.pack >actual &&
 	test_cmp expect actual
 '
 
-test_expect_success PERL_TEST_HELPERS 'negative depth disables deltas' '
+test_expect_success 'negative depth disables deltas' '
 	pack=$(git pack-objects --all --depth=-1 </dev/null pack) &&
 	echo 0 >expect &&
 	max_chain pack-$pack.pack >actual &&