emugl: Remove extraneous exit messasge with '-gpu mesa'.

The message "Could not remove native sub-window ..." was always displayed
when quitting normally the emulator with Mesa GPU emulation enabled. This
error message is here to catch real bug and should not be displayed in this
case.

Change-Id: I90768eb867fe5bbb309b48b427ecfa3f35bc804e
1 file changed