stake-pool: Deactivating Validator With Less Than 2x Min Delegation (OS-SSP-SUG-02)

[joncinque]

From OS-SSP-SUG-02:

Description

Deactivating a validator requires reducing its active stake to the minimum delegation first. However, in-
crease and Decrease Validator Stake instructions require a minimum of the same minimum_stake
amount. So, for example, a validator at 1.9x min delegation would require the following sequence to
deactivate:

1. IncreaseValidatorStake - bring amount to 2.9x min delegation
2. DecreaseValidatorStake - reduce amount to 1.0x min delegation
3. RemoveValidatorFromPool

Remediation

For ease of validator removal, consider allowing a validator to be removed if they have <= 2x minimum
delegation instead of the current <= 1x minimum delegation.