Build: drop acinclude.m4 never ever used by pacemaker proper

It was rather used by the management tool being part of heartbeat
project -- pacemaker's precursor -- hence the shared codebase that
just wasn't split carefully.

[note that hearbeat also mistakenly carries that file along while
the reason disappeared as of:
http://hg.linux-ha.org/heartbeat-STABLE_3_0/rev/cf17a3d4167b#l1.39]