varobj: Cleanup dead code

varobj: Cleanup dead code

This patch removes some dead code.

I noticed that varobj_delete was always called with dellist == NULL, so
I started removing that parameter.  That allows removing a good chunk of
the code in varobj_delete, making it almost trivial.  We can also remove
the resultp parameters in that whole trail.  In turn, this shows that
struct cpstack, cppush and cppop were only used fo that mechanism, so
they can be removed as well.

I also moved the function comment to the header file to comply with
today's guideline, even though the rest of the file does not respect it
(yet).

gdb/ChangeLog:

	* varobj.h (varobj_delete): Remove dellist parameter, update and
	move documentation here.
	* varobj.c (struct cpstack, cppush, cppop): Remove.
	(delete_variable): Remove resultp (first) parameter.
	(delete_variable_1): Likewise.
	(varobj_delete): Remove dellist parameter and unused code.
	(update_dynamic_varobj_children): Adjust varobj_delete call.
	(update_type_if_necessary): Likewise.
	(varobj_set_visualizer): Likewise.
	(varobj_update): Likewise.
	(value_of_root): Likewise.
	(varobj_invalidate_iter): Likewise.
	* mi/mi-cmd-var.c (mi_cmd_var_delete): Likewise.