- Clean up plancontext/fs.go code

- remove `@dagger(notimplemented)` from `engine.#Scratch`

Signed-off-by: Joel Longtine <joel@dagger.io>

plancontext/fs.go

@@ -33,13 +33,9 @@ func (fs *FS) Result() bkgw.Reference {
 	return fs.result
 }
 
-// func (fs *FS) FS() *solver.BuildkitFS {
-// 	return solver.NewBuildkitFS(fs.result)
-// }
-
 func (fs *FS) State() (llb.State, error) {
 	if fs.Result() == nil {
-		return llb.State{}, nil
+		return llb.Scratch(), nil
 	}
 	return fs.Result().ToState()
 }