mm/memremap_pages: Kill unused __devm_memremap_pages()

Kill this definition that was introduced in commit 41e94a8513 ("add
devm_memremap_pages") add never used.

Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/158041476158.3889308.4221100673554151124.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

include/linux/io.h

@@ -77,8 +77,6 @@ void *devm_memremap(struct device *dev, resource_size_t offset,
 		size_t size, unsigned long flags);
 void devm_memunmap(struct device *dev, void *addr);
 
-void *__devm_memremap_pages(struct device *dev, struct resource *res);
-
 #ifdef CONFIG_PCI
 /*
  * The PCI specifications (Rev 3.0, 3.2.5 "Transaction Ordering and