remove r_keep_alive and let keep_alive decide irg based on the node

include/libfirm/ircons.h

@@ -1726,7 +1726,6 @@ FIRM_API void set_r_store(ir_graph *irg, ir_node *store);
  * @param ka The node to keep alive.
  */
 FIRM_API void keep_alive(ir_node *ka);
-FIRM_API void r_keep_alive(ir_graph *irg, ir_node *ka);
 
 /* --- initialize and finalize IR construction --- */
 

ir/ir/ircons.c

@@ -716,14 +716,10 @@ void set_store(ir_node *store)
 	set_r_store(current_ir_graph, store);
 }
 
-void r_keep_alive(ir_graph *irg, ir_node *ka)
-{
-	add_End_keepalive(get_irg_end(irg), ka);
-}
-
 void keep_alive(ir_node *ka)
 {
-	r_keep_alive(current_ir_graph, ka);
+	ir_graph *irg = get_irn_irg(ka);
+	add_End_keepalive(get_irg_end(irg), ka);
 }
 
 void ir_set_uninitialized_local_variable_func(