ndtest: Cleanup all of blk namespace specific code

With the nd_namespace_blk and nd_blk_region infrastructures being removed,
the ndtest still has some references to the old code. So the
compilation fails as below,

../tools/testing/nvdimm/test/ndtest.c:204:25: error: ‘ND_DEVICE_NAMESPACE_BLK’ undeclared here (not in a function); did you mean ‘ND_DEVICE_NAMESPACE_IO’?
  204 |                 .type = ND_DEVICE_NAMESPACE_BLK,
      |                         ^~~~~~~~~~~~~~~~~~~~~~~
      |                         ND_DEVICE_NAMESPACE_IO
../tools/testing/nvdimm/test/ndtest.c: In function ‘ndtest_create_region’:
../tools/testing/nvdimm/test/ndtest.c:630:17: error: ‘ndbr_desc’ undeclared (first use in this function); did you mean ‘ndr_desc’?
  630 |                 ndbr_desc.enable = ndtest_blk_region_enable;
      |                 ^~~~~~~~~
      |                 ndr_desc
../tools/testing/nvdimm/test/ndtest.c:630:17: note: each undeclared identifier is reported only once for each function ...