Simplifying the Hello Facebook sample

Summary: per title

Test Plan: ran app

Reviewers: clang, chrisp, gregschechte

Reviewed By: gregschechte

CC: msdkexp@

Differential Revision: https://phabricator.fb.com/D583796

samples/HelloFacebookSample/HelloFacebookSample/HFViewController.m

@@ -154,7 +154,7 @@ - (IBAction)postStatusUpdateClick:(UIButton *)sender {
 
     // if it is available to us, we will post using the native dialog
     BOOL displayedNativeDialog = [FBNativeDialogs presentShareDialogModallyFrom:self
-                                                                    initialText:message
+                                                                    initialText:nil
                                                                           image:nil
                                                                             url:nil
                                                                         handler:nil];