Remove munmap_listp_free_cleanup

Remove munmap_listp_free_cleanup

This removes munmap_listp_free_cleanup, replacing it with a
std::unique_ptr at one spot and an explicit delete in another.  It
seemed simplest to completely change this data structure.

gdb/ChangeLog
2018-09-18  Tom Tromey  <tom@tromey.com>

	* compile/compile-object-run.c (do_module_cleanup): Use delete.
	* compile/compile-object-load.c (struct munmap_list): Move to
	header file.
	(munmap_list::add): Rename from munmap_list_add; rewrite.
	(munmap_list::~munmap_list): Rename from munmap_list_free.
	(munmap_listp_free_cleanup): Remove.
	(compile_object_load): Update.
	* compile/compile-object-load.h (struct munmap_list): Move from
	compile-object-load.c.  Rewrite.