libmsc/msc_a.c: fix: remove dummy allstate_action of msc_a_fsm

Since [1] has been merged to libosmocore, it was discovered that
the 'msc_a' FSM has a dummy 'allstate_action' handler assigned,
but 'allstate_event_mask' is 0x00 at the same time.

It basically doesn't make any sense, and moreover does cause
warnings and build failures.

[1] https://git.osmocom.org/libosmocore/commit/?id=b3f94eb39e19366c3458643ee329a73155d46ff8
[1] https://gerrit.osmocom.org/#/c/libosmocore/+/14361/

Change-Id: Ieb81b7a07ced1c40ba70d2adb0df68160ee62118
1 file changed