when insurance is under 5.75% of chunk size, then un-delegate it.
now we can make sure that during unbonding or re-delegation period, there must be no case where un-pairing insurance cannot cover penalty.

remainings:
* fix broken tests
* remove re-delegation info's deletable and amt field
* add tcs for new logics.

when calc penaltyAmt, must check shares value based on amt.

Those fields are introduced to cover the situation where unpairing ins at previous epoch cannot cover the penalty during re-delegation period.
But now we check paired ins with IsEnoughToCoverSlash so we don't need PenaltyAmt and Deletable anymore. Because that scenario will not happen.

* panic when validator is invalid (this must not happen)
* remove empty branch
* fix wrong calc in IsEnoughToCoverSlash

feedbacks:
* #9 (comment)
* #9 (comment)

by adding IsEnoughToCoverSlash function, the edge cases we were previously worried about are gone.
(unpairing ins at previous epoch cannot cover the penalty during re-delegation period).

so comments and checking logics for that edge should be deleted as now.

updated spec related with this pr

remove tc created during test locally

change function name of mustDelegate
mustDelegatePenaltyAmt is more readable and meaningful

Co-authored-by: dongsam <dongsamb@gmail.com>

Co-authored-by: dongsam <dongsamb@gmail.com>