logd: don't check of the timestamp of audit messages is monotonic

This is the last isMonotonic() user and can go away.  This timestamp
is set in the kernel source in either the audit_get_stamp() or
__audit_syscall_entry() functions.  In both cases, the value used is
from ktime_get_coarse_real_ts64(), which is a realtime timestamp.

Test: audit messages show in the log correctly.
Change-Id: Ife6c09dd97fccdfc7a8f07ee63161079ae2eccc4