Remove stale "cr" MPI extension

Checkpoint restart support was removed starting with commit 2192530.

Signed-off-by: Jeff Squyres <[email protected]>

Author: jsquyres

README

@@ -680,9 +680,6 @@ Open MPI Extensions
   - affinity: Provides the OMPI_Affinity_str() routine on retrieving
     a string that contains what resources a process is bound to.  See
     its man page for more details.
-  - cr: Provides routines to access to checkpoint restart routines.
-    See ompi/mpiext/cr/mpiext_cr_c.h for a listing of available
-    functions.
   - cuda: When the library is compiled with CUDA-aware support, it provides
     two things.  First, a macro MPIX_CUDA_AWARE_SUPPORT. Secondly, the
     function MPIX_Query_cuda_support that can be used to query for support.