Allow all bureaucrats to remove interface-admin

Seems harmless (unlike removing sysop which might cause bad social
dynamics), makes the config simpler, could come handy in an emergency
if an account is taken over.

Partially reverts commit 21b8ba5debcc8cac34fd97d7670f4d4913775421.

Change-Id: Ice2479f520fe37b676d1864e3fe801a289afe779