[ValSet]: Implement proper undelegate method

[czarcas7ic]

Background

https://github.com/osmosis-labs/osmosis/pull/6685 implements a method that takes into consideration the user's current delegations to their validator set.

We should continue the implementation of the original undelegate method to stick to the validator set, regaurdless of the composition of the user's current delegations. This involves making steps 5-7 reachable, and thoroughly testing this.

Additionally, the CLI and message server methods should be re-enabled once this method is working as intended.

Suggested Design

TBD

Acceptance Criteria

TBD