Clean up dead patterns, splitters, expanders and peepholes on the H8 port.

Clean up dead patterns, splitters, expanders and peepholes on the H8 port.

	* config/h8300/h8300.md (cpymemsi, movmd): Remove dead patterns,
	expanders, splits, etc.
	(movmd_internal_<mode>, movmd splitter, movstr, movsd): Likewise.
	(stpcpy_internal_<mode>, stpcpy splitter): Likewise.
	(peepholes to convert QI/HI mode pushes to SI mode pushes): Likewise.
	* config/h8300/h8300.c (h8300_swap_into_er6): Remove unused function.
	(h8300_swap_out_of_er6, h8sx_emit_movmd): Likewise
	* config/h8300/h8300-protos.h (h8300_swap_into_er6): Remove unused
	function prototype.
	(h8300_swap_out_of_er6, h8sx_emit_movmd): Likewise.