corelib: Remove Q_WS-macros.

corelib: Remove Q_WS-macros.

Q_WS_QPA is the only active code path after merging
refactor, other Q_WS-macros are no longer used.

Enable compilation without -qpa.

- Remove Q_OS_MSDOS, Q_OS_OS2
- Remove Q_WS_QWS
- Remove/replace definitions/conditionals of Q_WS_XX
- Remove qpa branches from profiles
- Replace Q_WS_MAC by  Q_OS_MAC
- Replace Q_WS_MAC && !Q_WS_QPA by
  Q_OS_MAC && !QT_NO_CORESERVICES
- Similarly in profiles: mac:contains(QT_CONFIG, coreservices)
- Replace Q_FS_FAT by Q_OS_WIN

Change-Id: Icce5a6c55b052c8f72b3b979ddf31a4f388ea9c9
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>