QWindowsMimeImage: Revert image format handling back to Qt 4.

QWindowsMimeImage: Revert image format handling back to Qt 4.

Effectively revert 9150563940f61be9fb17510be49c0734244866a5 for
QTBUG-11463 (offering only CF_DIB5 for images of format ARGB32) and
4018cd3529ded32f3434095a2da2568d52dfe16a for QTBUG-46848 adding support
for "PNG".

The changes broke pasting images into MS Office since it can only handle
plain CF_DIB and gets confused if "PNG" is returned as available format.

Task-number: QTBUG-47656
Task-number: QTBUG-11463
Task-number: QTBUG-46848
Change-Id: I9b641b4b912b7b16a2f58bc84fa09c28a64e91c8
Reviewed-by: aavit <eirik.aavitsland@theqtcompany.com>