Remove WIF support in --wallet argument

[532910]

I believe there should be no way to pass a sensitive data as a command line argument.

[alexvanin]

--wif is removed in v0.27.5. You still able to provide WIF with --wallet but it is less encouraged this way. Indeed, it is not secure, but it is useful for testing (e.g. neofs-testcases uses it a lot).

Config is tightly coupled with arguments, it will be hard to keep WIF in config but remove it from arguments.

I guess we will drop WIF support completely one day.

[carpawell]

We are ready.

[acid-ant]

@carpawell, @fyrchik, @realloc should we reject NEP2 together with WIF and read only from file?

[fyrchik]

I think NEP2 support can also be dropped, I haven't never seen it being actually used anywhere.