Widgets gallery: fix for mismatched @Composable annotation (#3402)

* Widgets gallery: fix for mismatched @Composable annotation

* Widgets gallery: remove isSystemInDarkTheme expect function

examples/widgets-gallery/shared/src/androidMain/kotlin/org/jetbrains/compose/demo/widgets/platform/System.kt

@@ -1,8 +0,0 @@
-package org.jetbrains.compose.demo.widgets.platform
-
-import androidx.compose.runtime.Composable
-import androidx.compose.foundation.isSystemInDarkTheme as androidSystemIsInDarkTheme
-
-@Composable
-actual fun isSystemInDarkTheme(): Boolean =
-    androidSystemIsInDarkTheme()

examples/widgets-gallery/shared/src/commonMain/kotlin/org/jetbrains/compose/demo/widgets/platform/System.kt

@@ -1,3 +0,0 @@
-package org.jetbrains.compose.demo.widgets.platform
-
-expect fun isSystemInDarkTheme(): Boolean

examples/widgets-gallery/shared/src/commonMain/kotlin/org/jetbrains/compose/demo/widgets/theme/Theme.kt

@@ -5,7 +5,7 @@ import androidx.compose.material.darkColors
 import androidx.compose.material.lightColors
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.graphics.Color
-import org.jetbrains.compose.demo.widgets.platform.isSystemInDarkTheme
+import androidx.compose.foundation.isSystemInDarkTheme
 import org.jetbrains.compose.demo.widgets.theme.ColorPallet.*
 
 // dark palettes

examples/widgets-gallery/shared/src/iosMain/kotlin/org/jetbrains/compose/demo/widgets/platform/System.kt

@@ -1,7 +0,0 @@
-package org.jetbrains.compose.demo.widgets.platform
-
-import androidx.compose.runtime.Composable
-import org.jetbrains.skiko.SystemTheme
-
-@Composable
-actual fun isSystemInDarkTheme(): Boolean = org.jetbrains.skiko.currentSystemTheme == SystemTheme.DARK