Make QFontEngineQPA report the TT 'cmap' table support

The QPF2 CMap is identical to the TrueType CMap table format.

Change-Id: I8c34d7c6a5942375538f3b8cb71d5a808b4fb400
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
QFontEngineQPA: Get rid of unused externalCMap

It seems to be a leftover after dropping the QPF1 font engine.

Change-Id: If8d3e1447fab9d042a85195d7bdb4d9811c37c6e
Reviewed-by: Lars Knoll <lars.knoll@digia.com>