stc12+: drop checksum verification for flashing

It's not needed on STC12 and up. All transfers are error checked with
parity and a 16-bit modular sum already. STC15 dropped the verification
checksum on the protocol level, it's not sent with the write status
packet, which is a testament to it being useless.

Some parts store the UID in the last bytes of flash memory and this
verification actually caused incorrect verification failures because
of that.

Fixes grigorig/stcgal#15.

stcgal/protocols.py

@@ -891,8 +891,6 @@ class Stc12BaseProtocol(StcBaseProtocol):
             response = self.read_packet()
             if response[0] != 0x00:
                 raise StcProtocolException("incorrect magic in write packet")
-            elif response[1] != csum:
-                raise StcProtocolException("verification checksum mismatch")
             print(".", end="")
             sys.stdout.flush()
         print(" done")