Build: configure: drop support for --with-acl option

--with-acl=no has been broken since 1.1.16 due to causing compiler warnings
about undefined functions.

We could fix it, but obviously no one cares, and ACLs don't require any special
libraries, so the only benefit would be a performance boost, at the expense of
using code that's never tested.

The only possible negative effect would be on users who explicitly use
--with-acl=yes, but they should be able to figure that out easily enough.