t0301-credential-cache: use 'test_atexit' to stop the credentials helper

Use 'test_atexit' to run cleanup commands to stop the credentials
helper at the end of the test script or upon interrupt or failure, as
it is shorter, simpler, and more robust than registering such cleanup
commands in the trap on EXIT in the test scripts.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0301-credential-cache.sh

@@ -10,7 +10,7 @@ test -z "$NO_UNIX_SOCKETS" || {
 }
 
 # don't leave a stale daemon running
-trap 'code=$?; git credential-cache exit; (exit $code); die' EXIT
+test_atexit 'git credential-cache exit'
 
 # test that the daemon works with no special setup
 helper_test cache
@@ -108,9 +108,4 @@ test_expect_success SYMLINKS 'use user socket if user directory is a symlink to
 
 helper_test_timeout cache --timeout=1
 
-# we can't rely on our "trap" above working after test_done,
-# as test_done will delete the trash directory containing
-# our socket, leaving us with no way to access the daemon.
-git credential-cache exit
-
 test_done