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.

(cherry picked from commit c1bfaa22)

Bug: 18609574
Change-Id: Iefc3c51be35ceaff0031522c4d6c2cdf5703dcb6