Allow contract migration to multisigned transaction from Alphabet

[alexvanin]

Migrate methods can be invoked only by "contract owner", which is set manually at deploy. This is not quite secure to have single wallet with contract owner, because this wallet can be unrelated to NeoFS in the first place. Instead we can check witness of alphabet multi signature before contract migration. The other option is to check committee witness.

In this case we can remove owner argument from contract deployment routines.