x86: Remove pci-nommu.c

The commit that switched x86 to dma_direct_ops stopped using and building
this file, but accidentally left it in the tree.  Remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: iommu@lists.infradead.org
Link: https://lkml.kernel.org/r/20180416124442.13831-1-hch@lst.de