esp8266: Rename "machine" module implementation to use contemporary naming.

Previously they used historical "pyb" affix causing confusion and
inconsistency (there's no "pyb" module in modern ports; but people
took esp8266 port as an example, and "pyb" naming kept proliferating,
while other people complained that source structure is not clear).

esp8266/modutime.c

@@ -34,8 +34,7 @@
 #include "py/runtime.h"
 #include "py/mphal.h"
 #include "py/smallint.h"
-#include "modpyb.h"
-#include "modpybrtc.h"
+#include "modmachine.h"
 #include "timeutils.h"
 #include "user_interface.h"
 #include "extmod/utime_mphal.h"