selftests/landlock: Fully test file rename with "remove" access

These tests were missing to check the check_access_path() call with all
combinations of maybe_remove(old_dentry) and maybe_remove(new_dentry).

Extend layout1.link with a new complementary test and check that
REMOVE_FILE is not required to link a file.

Cc: Shuah Khan <shuah@kernel.org>
Link: https://lore.kernel.org/r/20220506160820.524344-7-mic@digikod.net


Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>