Removes unnecessary .Index field of FunctionInstance (#1270)

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

internal/wasm/module.go

@@ -604,7 +604,6 @@ func (m *ModuleInstance) BuildFunctions(mod *Module, importedFunctions []*Functi
 		fns[offset] = FunctionInstance{
 			TypeID:     m.TypeIDs[section],
 			Module:     m,
-			Idx:        d.index,
 			Type:       d.funcType,
 			Definition: d,
 		}

internal/wasm/store.go

@@ -114,9 +114,6 @@ type (
 		// TypeID is assigned by a store for FunctionType.
 		TypeID FunctionTypeID
 
-		// Idx holds the index of this function instance in the function index (beginning with imports).
-		Idx Index
-
 		// Definition is known at compile time.
 		Definition api.FunctionDefinition
 	}