[QFontDatabase] Get rid of QtFontEncoding

This one has not been unsed for ages (since Qt3?).

Change-Id: Iaf514db1b698b34a303f34c150b72db989eb176c
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>