io/input,io/transfer: [API] replace OfferOp with command

Also delete two tests that are no longer relevant.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

internal/ops/ops.go

@@ -67,7 +67,6 @@ const (
 	TypeClipboardWrite
 	TypeSource
 	TypeTarget
-	TypeOffer
 	TypeKeyInput
 	TypeSave
 	TypeLoad
@@ -148,7 +147,6 @@ const (
 	TypeClipboardWriteLen   = 1
 	TypeSourceLen           = 1
 	TypeTargetLen           = 1
-	TypeOfferLen            = 1
 	TypeKeyInputLen         = 1 + 1
 	TypeSaveLen             = 1 + 4
 	TypeLoadLen             = 1 + 4
@@ -427,7 +425,6 @@ var opProps = [0x100]opProp{
 	TypeClipboardWrite:   {Size: TypeClipboardWriteLen, NumRefs: 1},
 	TypeSource:           {Size: TypeSourceLen, NumRefs: 2},
 	TypeTarget:           {Size: TypeTargetLen, NumRefs: 2},
-	TypeOffer:            {Size: TypeOfferLen, NumRefs: 3},
 	TypeKeyInput:         {Size: TypeKeyInputLen, NumRefs: 2},
 	TypeSave:             {Size: TypeSaveLen, NumRefs: 0},
 	TypeLoad:             {Size: TypeLoadLen, NumRefs: 0},
@@ -498,8 +495,6 @@ func (t OpType) String() string {
 		return "Source"
 	case TypeTarget:
 		return "Target"
-	case TypeOffer:
-		return "Offer"
 	case TypeKeyInput:
 		return "KeyInput"
 	case TypeSave: