Remove dex2oat watchdog warning

The warning output is breaking vm-tests on some devices. It does not
seem to serve much of a purpose given that it does not go to logcat
and long running compiles can be identified by the time summary
printed at the end of dex2oat.

Bug: 18609574
Change-Id: Ic4f3d118d99e4b307cbb7c4c2b57f05a003e092e