remove redundant dir desktopMain (#8)

desktopMain/kotlin/main.desktop.kt

@@ -1,12 +0,0 @@
-import androidx.compose.desktop.ui.tooling.preview.Preview
-import androidx.compose.runtime.Composable
-
-actual fun getPlatformName(): String = "Desktop"
-
-@Composable fun MainView() = App()
-
-@Preview
-@Composable
-fun AppPreview() {
-    App()
-}