udevadm: drop pointless must_be_root() checks

udevadm: drop pointless must_be_root() checks

Checking if we are root on the client side is generally pointless, since the
privileged operation will fail anyway and we can than log what precisly went
wrong.

A check like this makes sense only if:
- we need to do some expensive unprivileged operation before attempting the
  privileged operation, and the check allows us avoid wasting resources.
- the privileged operation would fail but in an unclear way.

Neither of those cases applies here.

This fixes calls like 'udevadm control -h' as unprivileged user.