logd: handle uidToName() directly

uidToName() originally used a separate worker thread with additional
group permissions.  Threads are not security boundaries however, so
these group permissions are removed in a previous change.

This change handles the lookup for uidToName() directly without using
a separate thread.

Test: boot CF, logd unit tests
Change-Id: If245388bc221bc77102a0bbcee82c8f42b140760