um: page_offset.h is never used

... and neither is the only define in it

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/page_offset.h

@@ -1 +0,0 @@
-#define PAGE_OFFSET_RAW (uml_physmem)