Simplify post epilogue_completed splitters.

Simplify post epilogue_completed splitters.

Now that we have post epilogue_completed split point for all
optimization levels, we can simplify post epilogue_completed splitters
considerably. If corresponding define_peephole2 pattern fails to
allocate a temporary register (or if peephole2 pass isn't run at all),
we can now always split invalid RTX after epilogue_completed is set.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

	* config/i386/i386.md (*pushdi2_rex64 peephole2): Remove.
	(*pushdi2_rex64 peephole2): Unconditionally split after
	epilogue_completed.
	(*ashl<mode>3_doubleword): Ditto.
	(*<shift_insn><mode>3_doubleword): Ditto.