Remove handleSynchronous* functions.

Remove handleSynchronous* functions.

There are now two different ways to implement synchronous
event processing. The platform plugins can choose which
one to use.

1) flushWindowSystemEvents()
   Use to flush the event queue at one point, making
   preceding calls synchronous.

2) setSynchronousWindowsSystemEvents(bool enable)
   Makes all handle* functions synchronous, bypassing
   the event queue completely.

Change-Id: I020b80c731fd13f855a377d7c91d06a4e39b6a0b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>