sweep: remove FeeRate() from InputSet interface

As shown in the following commit, fee rate calculation will now be
handled by the fee bumper, hence there's no need to expose this on
`InputSet` interface.

sweep/tx_input_set.go

@@ -51,9 +51,6 @@ type InputSet interface {
 	// Inputs returns the set of inputs that should be used to create a tx.
 	Inputs() []input.Input
 
-	// FeeRate returns the fee rate that should be used for the tx.
-	FeeRate() chainfee.SatPerKWeight
-
 	// AddWalletInputs adds wallet inputs to the set until a non-dust
 	// change output can be made. Return an error if there are not enough
 	// wallet inputs.
@@ -208,11 +205,6 @@ func (t *txInputSet) DeadlineHeight() fn.Option[int32] {
 	return fn.None[int32]()
 }
 
-// FeeRate returns the fee rate that should be used for the tx.
-func (t *txInputSet) FeeRate() chainfee.SatPerKWeight {
-	return t.feeRate
-}
-
 // NeedWalletInput returns true if the input set needs more wallet inputs.
 func (t *txInputSet) NeedWalletInput() bool {
 	return !t.enoughInput()
@@ -807,12 +799,3 @@ func (b *BudgetInputSet) Inputs() []input.Input {
 
 	return inputs
 }
-
-// FeeRate returns the fee rate that should be used for the tx.
-//
-// NOTE: part of the InputSet interface.
-//
-// TODO(yy): will be removed once fee bumper is implemented.
-func (b *BudgetInputSet) FeeRate() chainfee.SatPerKWeight {
-	return 0
-}