Dashboard: Remove "Try Gutenberg" callout.

Reverting this for 4.9. It will be added back in a future version of WordPress. This doesn't mean that you shouldn't be trying Gutenberg, just that it isn't ready for a call out to a larger audience. But if you are the type to read commit messages, https://github.com/WordPress/gutenberg could use your pull requests and comments on issues.

Reverts [41931] [41900] [41896] [41895]
See #41316


Built from https://develop.svn.wordpress.org/trunk@41978


git-svn-id: http://core.svn.wordpress.org/trunk@41812 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/default-filters.php

@@ -318,7 +318,6 @@ add_action( 'transition_post_status',     '_transition_post_status',
 add_action( 'transition_post_status',     '_update_term_count_on_transition_post_status', 10, 3 );
 add_action( 'comment_form',               'wp_comment_form_unfiltered_html_nonce'          );
 add_action( 'admin_init',                 'send_frame_options_header',               10, 0 );
-add_action( 'try_gutenberg_panel',        'wp_try_gutenberg_panel'                         );
 add_action( 'welcome_panel',              'wp_welcome_panel'                               );
 
 // Cron tasks

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-beta3-41977';
+$wp_version = '4.9-beta3-41978';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.