QCoreTextFontDatabase: Remove number type asserts.

On iOS 8, the value 0 is returned as a kCFNumberIntType.
The code still works - CFNumberGetValue converts it
to a 0.0 double.

Change-Id: Ic50900b22e4fa19ad1481e8e0e293559bbfd8cd2
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

Conflicts:
	src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm