The workaround for wrong pager aspect ratio in the deskbar mode breaks D&D
in the pager and may produce infinite looping (currently it is stable
but that may change with even small changes to the pager requisition/allocation
mechanism).

This commit removes the workaround, which means that:
- the pager aspect ratio in the deskbar mode is only correct when
  libwnck >=2.31.0 is used
- D&D in the pager works again as in panel 4.8.
(cherry picked from commit 67b419fb91e8ffa25d6af25488e75f0d610a54b9)