t/t{3600,3800,5401}: do not use egrep when grep would do

There is nothing _wrong_ with egrep per se, but this way we
would have less dependency on external tools.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3600-rm.sh

@@ -127,7 +127,7 @@ test_expect_success '"rm" command printed' '
 	git add test-file &&
 	git commit -m "add file for rm test" &&
 	git rm test-file > rm-output &&
-	test `egrep "^rm " rm-output | wc -l` = 1 &&
+	test `grep "^rm " rm-output | wc -l` = 1 &&
 	rm -f test-file rm-output &&
 	git commit -m "remove file from rm test"
 '

t/t3800-mktag.sh

@@ -15,7 +15,7 @@ check_verify_failure () {
     test_expect_success \
         "$1" \
         'git-mktag <tag.sig 2>message ||
-         egrep -q -f expect.pat message'
+        grep -q -f expect.pat message'
 }
 
 ###########################################################

t/t5401-update-hooks.sh

@@ -129,7 +129,7 @@ STDOUT post-update
 STDERR post-update
 EOF
 test_expect_success 'send-pack stderr contains hook messages' '
-	egrep ^STD send.err >actual &&
+	grep ^STD send.err >actual &&
 	git diff - actual <expect
 '