libnvdimm/pmem: Delete include of nd-core.h

The entire point of nd-core.h is to hide functionality that no leaf
driver should touch. In fact, the commit that added it had no need to
include it.

Fixes: 06e8ccda ("acpi: nfit: Add support for detect platform...")
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>