txscript: Make op callbacks take opcode and data.

This converts the callback function defined on the internal opcode
struct to accept the opcode and data slice instead of a parsed opcode as
the final step towards removing the parsed opcode struct and associated
supporting code altogether.

It also updates all of the callbacks and tests accordingly and finally
removes the now unused parsedOpcode struct.

txscript/engine.go

@@ -378,15 +378,14 @@ func (vm *Engine) executeOpcode(op *opcode, data []byte) error {
 	// Ensure all executed data push opcodes use the minimal encoding when
 	// the minimal data verification flag is set.
 	if vm.dstack.verifyMinimalData && vm.isBranchExecuting() &&
-		pop.opcode.value >= 0 && pop.opcode.value <= OP_PUSHDATA4 {
+		op.value >= 0 && op.value <= OP_PUSHDATA4 {
 
 		if err := checkMinimalDataPush(op, data); err != nil {
 			return err
 		}
 	}
 
-	pop := parsedOpcode{opcode: op, data: data}
-	return op.opfunc(&pop, vm)
+	return op.opfunc(op, data, vm)
 }
 
 // checkValidPC returns an error if the current script position is not valid for