Enable compilation without -qpa.

- Remove conditionals from Q_WS_QPA sections.
- Rename precompiled header.
- Remove gui-related Q_OS_SYMBIAN-#ifdef sections.
- Leave other Q_WS code in for reference.

Change-Id: I16326b631fff483aec8edd2f7a2e7a1822eab814
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>