Remove dead assignment, but why...

This assignment isn't doing anything, so it safe to remove it, but
there remains the question of whether there could have been some
actually necessary intention behind this line.

src/switch_channel.c

@@ -3919,8 +3919,6 @@ SWITCH_DECLARE(char *) switch_channel_expand_variables_check(switch_channel_t *c
 						idx = atoi(ptr);
 					}
 					
-					if (!sub_val) sub_val = vname;
-
 					if ((sub_val = (char *) switch_channel_get_variable_dup(channel, vname, SWITCH_TRUE, idx))) {
 						if (var_list && !switch_event_check_permission_list(var_list, vname)) {
 							sub_val = "<Variable Expansion Permission Denied>";