Revert "Getting DeepEqual to work with maps whose key is an interface (#4360)"

This reverts commit 1fd75ffbda.

The change is not correct and allows code to continue while it should
panic. For details, see:
https://github.com/tinygo-org/tinygo/pull/4360#issuecomment-2252943012

src/reflect/value.go

@@ -982,9 +982,7 @@ func (v Value) MapIndex(key Value) Value {
 	vkey := v.typecode.key()
 
 	// compare key type with actual key type of map
-	// AssignableTo is not implemented for interfaces
-	// avoid: "reflect: unimplemented: AssignableTo with interface"
-	if vkey.Kind() != Interface && !key.typecode.AssignableTo(vkey) {
+	if !key.typecode.AssignableTo(vkey) {
 		// type error?
 		panic("reflect.Value.MapIndex: incompatible types for key")
 	}