Improve xbps_end() and use it before exit(3)ing.

- Simplify xbps_repo_open::repo_get_dict().
- Use xbps_end() in the utils where necessary.
- Make xbps_end() call xbps_pkgdb_unlock() if necessary.
- Make xbps_end() release rpool resources.
- Make xbps_end() release resources from xbps_handle.
- Fixed 90% of reported leaks (still reachable at exit) from valgrind.

That was to silence valgrind's memcheck with --leak-check=full.

bin/xbps-query/main.c

@@ -296,5 +296,6 @@ main(int argc, char **argv)
 		rv = show_pkg_revdeps(&xh, pkg, repo_mode);
 	}
 
+	xbps_end(&xh);
 	exit(rv);
 }