native: don't push void result in Call

This was done in https://github.com/neo-project/neo/pull/1693
for native calls. `OnPersist` script still uses `DROP` though
as value is pushed via `CheckReturn` logic for regular calls.

pkg/core/interop/context.go

@@ -82,6 +82,7 @@ type Method = func(ic *Context, args []stackitem.Item) stackitem.Item
 // MethodAndPrice is a native-contract method descriptor.
 type MethodAndPrice struct {
 	Func          Method
+	MD            *manifest.Method
 	Price         int64
 	RequiredFlags smartcontract.CallFlag
 }
@@ -123,6 +124,7 @@ func NewContractMD(name string) *ContractMD {
 // AddMethod adds new method to a native contract.
 func (c *ContractMD) AddMethod(md *MethodAndPrice, desc *manifest.Method, safe bool) {
 	c.Manifest.ABI.Methods = append(c.Manifest.ABI.Methods, *desc)
+	md.MD = desc
 	c.Methods[desc.Name] = *md
 	if safe {
 		c.Manifest.SafeMethods.Add(desc.Name)