x86/Kconfig: Remove the unused X86_DMA_REMAP KConfig symbol

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190410080220.21705-2-hch@lst.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>