PHIOPT: Move store_elim_worker into pass_cselim::execute

This simple patch moves the body of store_elim_worker
direclty into pass_cselim::execute.

Also removes unneeded prototypes too.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (cond_store_replacement): Remove
	prototype.
	(cond_if_else_store_replacement): Likewise.
	(get_non_trapping): Likewise.
	(store_elim_worker): Move into ...
	(pass_cselim::execute): This.