Fix FFMPEG module dependencies.

vtkPVServerManagerDefault needs to depend on vtkIOFFMPEG. Fixed that.
Also removing the now redundant dependency on vtkIOFFMPEG in VTKModules.cmake.

Change-Id: I6ce71ca0d4b1a0cca02924da1b6fd7d0f0511793
Merge topic 'fix_ffmpeg_support' into next

ff234a2 Fix FFMPEG module dependencies.