t1301-shared-repo.sh: don't let a default ACL interfere with the test

t1301-shared-repo.sh: don't let a default ACL interfere with the test

This test creates files with several different umasks and expects their
permissions to be initialized according to the umask, so a default ACL on the
trash directory (which overrides the umask for files created in that directory)
causes the test to fail.  To avoid that, remove the default ACL if possible with
setfacl(1).

Signed-off-by: Matt McCutchen <matt@mattmccutchen.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>