Do the actual removal of the Soft Keys API and related code

Do the actual removal of the Soft Keys API and related code

In addition to the actual removal of the softkeys API in QAction,
this commit removes some enums related to the softkeys feature:
  Qt::WA_MergeSoftkeys
  Qt::WA_MergeSoftkeysRecursively

It also removes some "zombie" enums:
  Qt::WindowSoftkeysVisibleHint = 0x40000000,
  Qt::WindowSoftkeysRespondHint = 0x80000000,

  (The only implementation that used these were removed when
  qapplication_s60.cpp and qwidget_s60.cpp were removed.)

Change-Id: Ib6fc6d543def4757383d5f19256199d9d190c614
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Janne Anttila <janne.anttila@digia.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>