branch='off' is command to turn CNR mode off, while branch_off is status reflecting that it is off

See https://software.intel.com/en-us/mkl-developer-reference-c-named-constants-for-cnr-control

Hence, `mkl.cbwr_set('branch_off')` now raises an exception,
and the test is modified to query cnr_const='all' to allow cbwr_get to also see strict flag.

Author: oleksandr-pavlyk

mkl/_mkl_service.pyx

@@ -646,7 +646,6 @@ cdef object __cbwr_set(branch=None):
     __variables = {
         'input': {
             'off': mkl.MKL_CBWR_OFF,
-            'branch_off': mkl.MKL_CBWR_BRANCH_OFF,
             'auto': mkl.MKL_CBWR_AUTO,
             'compatible': mkl.MKL_CBWR_COMPATIBLE,
             'sse2': mkl.MKL_CBWR_SSE2,
@@ -690,7 +689,6 @@ cdef inline __cbwr_get(cnr_const=None):
             'all': mkl.MKL_CBWR_ALL,
         },
         'output': {
-            mkl.MKL_CBWR_OFF: 'off',
             mkl.MKL_CBWR_BRANCH_OFF: 'branch_off',
             mkl.MKL_CBWR_AUTO: 'auto',
             mkl.MKL_CBWR_COMPATIBLE: 'compatible',