py: Improve efficiency of MP_OBJ_IS_STR_OR_BYTES.

Saves ROM (16 on stmhal, 240 on 64-bit unix) and should be quicker since
there is 1 less branch.
diff --git a/py/objint.c b/py/objint.c
index a771383..c190c18 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -38,6 +38,7 @@
 #include "smallint.h"
 #include "mpz.h"
 #include "objint.h"
+#include "objstr.h"
 #include "runtime0.h"
 #include "runtime.h"