py: Use m_{new,renew,del} consistently.

This is so all memory requests go through the same interface.
diff --git a/py/objint.c b/py/objint.c
index 4a4a21a..0fb2a38 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -137,7 +137,7 @@
     print(env, "%s", str);
 
     if (buf != stack_buf) {
-        m_free(buf, buf_size);
+        m_del(char, buf, buf_size);
     }
 }