shared: do not include ~ when appending syscall filters property

The method already uses a boolean argument to determine whether it is in
whitelist mode or not. The code that will parse the string of filters
does not expect the ~, since it already has the boolean argument. Thus,
it will fail to parse the list of filters.

src/shared/bus-unit-util.c

@@ -966,7 +966,7 @@ static int bus_append_execute_property(sd_bus_message *m, const char *field, con
                 if (r < 0)
                         return bus_log_create_error(r);
 
-                for (p = eq;;) {
+                for (;;) {
                         _cleanup_free_ char *word = NULL;
 
                         r = extract_first_word(&p, &word, NULL, EXTRACT_QUOTES);