support channel sign without adding timestamp to signature

[tzarebczan]

Basically add a param to make this part optional -

lbry-sdk/lbry/extras/daemon/daemon.py

Line 2975 in 3e3974f

signature = signing_channel.sign_data(unhexlify(str(hexdata)), timestamp)

It can return a bogus release time

Odysee is trying to use these signatures as a URL parameter for verification of unlisted content, so we now need to pass both the signature and signingts, which makes the URL even longer.