x86, libnvdimm/test: Remove COPY_MC_TEST

The COPY_MC_TEST facility has served its purpose for validating the
early termination conditions of the copy_mc_fragile() implementation.
Remove it and the EXPORT_SYMBOL_GPL of copy_mc_fragile().

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/160316688322.3374697.8648308115165836243.stgit@dwillia2-desk3.amr.corp.intel.com