CppEditor: Remove unused function

Change-Id: I4ebcf66d39192cd099d7cdc6ec27e74837975ed3
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Move QtVersionsModel declaration into header

Change-Id: Ic61139ef5e8819bb0ae2ba67cfff6b5adc55c14d
Reviewed-by: Eike Ziller <eike.ziller@digia.com>