x/sequencers: document reason for only bonded sequencer able to reduce bond

[danwt]

dymension/x/sequencer/keeper/msg_server_increase_bond.go

Lines 49 to 52 in acd9d13

	// check if the sequencer is bonded
	if !sequencer.IsBonded() {
	return types.Sequencer{}, types.ErrInvalidSequencerStatus
	}

Needs explanation

[danwt]

superseded by #1328