esp8266: Remove pin_id field from C pin object.

This field is the same as phys_port and not needed.
diff --git a/esp8266/modpyb.h b/esp8266/modpyb.h
index eb67d5c..69a6edb 100644
--- a/esp8266/modpyb.h
+++ b/esp8266/modpyb.h
@@ -13,10 +13,9 @@
 
 typedef struct _pyb_pin_obj_t {
     mp_obj_base_t base;
-    uint16_t pin_id;
     uint16_t phys_port;
-    uint32_t periph;
     uint16_t func;
+    uint32_t periph;
 } pyb_pin_obj_t;
 
 uint mp_obj_get_pin(mp_obj_t pin_in);