uml: remove code made redundant by CHOOSE_MODE removal

This patch makes a number of simplifications enabled by the removal of
CHOOSE_MODE.  There were lots of functions that looked like

	int foo(args){
		foo_skas(args);
	}

The bodies of foo_skas are now folded into foo, and their declarations (and
sometimes entire header files) are deleted.

In addition, the union uml_pt_regs, which was a union between the tt and skas
register formats, is now a struct, with the tt-mode arm of the union being
removed.

It turns out that usr2_handler was unused, so it is gone.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/sys-x86_64/tls.c

@@ -11,7 +11,7 @@ int arch_copy_tls(struct task_struct *t)
 	 * (which is argument 5, child_tid, of clone) so it can be set
 	 * during context switches.
 	 */
-	t->thread.arch.fs = t->thread.regs.regs.skas.regs[R8 / sizeof(long)];
+	t->thread.arch.fs = t->thread.regs.regs.regs[R8 / sizeof(long)];
 
         return 0;
 }