py: Take out bitfield entries from their own structure.

Don't need to wrap bitfields in their own struct.  Compiler does the
correct thing without it.
diff --git a/py/map.h b/py/map.h
index ce55055..afebfda 100644
--- a/py/map.h
+++ b/py/map.h
@@ -4,11 +4,9 @@
 } mp_map_elem_t;
 
 typedef struct _mp_map_t {
-    struct {
-        machine_uint_t all_keys_are_qstrs : 1;
-        machine_uint_t table_is_fixed_array : 1;
-        machine_uint_t used : (8 * sizeof(machine_uint_t) - 2);
-    };
+    machine_uint_t all_keys_are_qstrs : 1;
+    machine_uint_t table_is_fixed_array : 1;
+    machine_uint_t used : (8 * sizeof(machine_uint_t) - 2);
     machine_uint_t alloc;
     mp_map_elem_t *table;
 } mp_map_t;