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 this not being needed.

Some parts store the UID in the last bytes of flash memory and this
verification actually caused incorrect verification failures because
of the verification, which apparently read the UID on verification
readback.

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")