py: Use mp_raise_msg helper function where appropriate.

Saves the following number of bytes of code space: 176 for bare-arm, 352
for minimal, 272 for unix x86-64, 140 for stmhal, 120 for esp8266.
diff --git a/py/parsenum.c b/py/parsenum.c
index 83a6abd..1010ad3 100644
--- a/py/parsenum.c
+++ b/py/parsenum.c
@@ -27,7 +27,7 @@
 #include <stdbool.h>
 #include <stdlib.h>
 
-#include "py/nlr.h"
+#include "py/runtime.h"
 #include "py/parsenumbase.h"
 #include "py/parsenum.h"
 #include "py/smallint.h"
@@ -55,7 +55,7 @@
     // check radix base
     if ((base != 0 && base < 2) || base > 36) {
         // this won't be reached if lex!=NULL
-        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "int() arg 2 must be >= 2 and <= 36"));
+        mp_raise_msg(&mp_type_ValueError, "int() arg 2 must be >= 2 and <= 36");
     }
 
     // skip leading space