send-pack: fix leaking common object IDs

We're leaking the array of common object IDs in `send_pack()`. Fix this
by creating a common exit path where we free the leaking data. While at
it, unify some other cleanups now that we have a central place to put
them.

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

t/t5549-fetch-push-http.sh

@@ -5,6 +5,7 @@ test_description='fetch/push functionality using the HTTP protocol'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd