t5703: replace "grep -a" usage by perl

On some platforms likes HP-UX, grep(1) doesn't understand "-a".
Let's switch to perl.

Signed-off-by: Đoàn Trần Công Danh <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: sgn

t/t5703-upload-pack-ref-in-want.sh

@@ -52,15 +52,18 @@ test_expect_success 'setup repository' '
 
 test_expect_success 'config controls ref-in-want advertisement' '
 	test-tool serve-v2 --advertise-capabilities >out &&
-	! grep -a ref-in-want out &&
+	perl -ne "/ref-in-want/ and print" out >out.filter &&
+	test_must_be_empty out.filter &&
 
 	git config uploadpack.allowRefInWant false &&
 	test-tool serve-v2 --advertise-capabilities >out &&
-	! grep -a ref-in-want out &&
+	perl -ne "/ref-in-want/ and print" out >out.filter &&
+	test_must_be_empty out.filter &&
 
 	git config uploadpack.allowRefInWant true &&
 	test-tool serve-v2 --advertise-capabilities >out &&
-	grep -a ref-in-want out
+	perl -ne "/ref-in-want/ and print" out >out.filter &&
+	test_file_not_empty out.filter
 '
 
 test_expect_success 'invalid want-ref line' '