Update onRestoreInstanceState function for API 31 migration

Author: irfano

app/src/main/kotlin/org/wordpress/aztec/demo/MainActivity.kt

@@ -511,15 +511,13 @@ open class MainActivity : AppCompatActivity(),
         }
     }
 
-    override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
+    override fun onRestoreInstanceState(savedInstanceState: Bundle) {
         super.onRestoreInstanceState(savedInstanceState)
 
         aztec.initSourceEditorHistory()
 
-        savedInstanceState?.let {
-            if (savedInstanceState.getBoolean("isMediaUploadDialogVisible")) {
-                showMediaUploadDialog()
-            }
+        if (savedInstanceState.getBoolean("isMediaUploadDialogVisible")) {
+            showMediaUploadDialog()
         }
     }