Remove the ability to update an account's VP

[cwgoes]

We do not need the ability for an account to update their VP in the initial version of Namada, and we should remove it.

[grarco]

Should we also remove the vp hash from InitAccount and just assign the default vp_user to all the established addresses?

[cwgoes]

Should we also remove the vp hash from InitAccount and just assign the default vp_user to all the established addresses?

Yes. Good catch.

[tzemanovic]

also rm the vp field from genesis::transactions::ValidatorAccountTx

[grarco]

Closing this as it seems we don't need it anymore