logd: don't coalesce identical log messages in the security buffer

This buffer isn't human readable and the parsers aren't set up to
handle the 'chatty' message for identical log messages.  Further, it
is a low volume buffer so there's not much in terms of memory saving
if this were enabled.

Bug: 137093665
Test: security unit tests
Change-Id: I03fce518d3308a6d9240bd29e83ff3237203fe3b