gdb: remove iterate_over_breakpoints function

Now that we have range functions that let us use ranged for loops, we
can remove iterate_over_breakpoints in favor of those, which are easier
to read and write.  This requires exposing the declaration of
all_breakpoints and all_breakpoints_safe in breakpoint.h, as well as the
supporting types.

Change some users of iterate_over_breakpoints to use all_breakpoints,
when they don't need to delete the breakpoint, and all_breakpoints_safe
otherwise.

gdb/ChangeLog:

	* breakpoint.h (iterate_over_breakpoints): Remove.  Update
	callers to use all_breakpoints or all_breakpoints_safe.
	(breakpoint_range, all_breakpoints, breakpoint_safe_range,
	all_breakpoints_safe): Move here.
	* breakpoint.c (all_breakpoints, all_breakpoints_safe): Make
	non-static.
	(iterate_over_breakpoints): Remove.
	* python/py-finishbreakpoint.c (bpfinishpy_detect_out_scope_cb):
	Return void.
	* python/py-breakpoint.c (build_bp_list): Add comment, reverse
	return value logic.
	* guile/scm-breakpoint.c (bpscm_build_bp_list): Return void.

Change-Id: Idde764a1f577de0423e4f2444a7d5cdb01ba5e48