c++, coroutines: Clean up the ramp cleanups.

This replaces the cleanup try-catch block in the ramp with a series of
eh-only cleanup statements.

Includes
 typo fixes from 83aa09e90487b52c1772eeffc4af577ee70536f1
 dead code removal from 7bba8d48ea556a03bdc4e9076740b83d3db6599e

gcc/cp/ChangeLog:

	* coroutines.cc (analyze_fn_parms): No longer
	create a parameter copy guard var.
	(cp_coroutine_transform::build_ramp_function): Replace ramp
	cleanup try-catch block with eh-only cleanup statements.
	* coroutines.h (struct param_info): Remove the
	entry for the parameter copy destructor guard.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit 18df4a10bc96946401218019ec566d867238b3e4)