BUG: Fix slowdown when reading large bin files.

In it's CanReadFile() vtkEnsembleReader was opening large binary files
entirely before determining that it can't read it. That cause incredible
slowdown when reading large bin files. Fixed that by removing
CanReadFile(). vtkEnsembleReader can just use extension matching to
determine if it can read the file.

Change-Id: Ic2b817ecd6e0e5cfdd5a1c5013a085a392640fef
Merge topic 'fix_file_open_slowdown' into next

b937dbf1 BUG: Fix slowdown when reading large bin files.