Remove simple_displaced_step_copy_insn

Remove simple_displaced_step_copy_insn

Nothing uses this function.  Remove it, and adjust comments referring to
it.

gdb/ChangeLog:

	* arch-utils.h (simple_displaced_step_copy_insn): Remove.
	* arch-utils.c (simple_displaced_step_copy_insn): Remove.
	* gdbarch.sh (displaced_step_copy_insn): Adjust comment.
	* gdbarch.h: Regenerate.
	* i386-linux-tdep.c (i386_linux_displaced_step_copy_insn):
	Adjust comment.
	* i386-tdep.c (i386_displaced_step_copy_insn): Adjust comment.
	(i386_displaced_step_fixup): Adjust comment.
	* rs6000-tdep.c (ppc_displaced_step_copy_insn): Adjust comment.