security: Remove integrity from the LSM list in Kconfig

Remove 'integrity' from the list of LSMs in Kconfig, as it is no longer
necessary. Since the recent change (set order to LSM_ORDER_LAST), the
'integrity' LSM is always enabled (if selected in the kernel
configuration).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>