Revert 99480d5420c0beea6771be582c039b550a4461f5

The Mac OS X platform plugin has been fixed so that this
hack is no longer needed. Not to mention that it breaks on XCB.

We keep the warning about bad exposes from the plugin in debug
mode. These are still useful for tracking down future bugs.

Task-number: QTBUG-35143
Change-Id: I5125f7ae2b7fd77c55e9a29b10aa5434598a9ea9
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>