Remove the help text under the sidebar subscribe button and style it inline

What does this MR do?

Remove the help text under the sidebar subscribe button and style it inline

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Current help text is over obvious and pushes references too far down. Also the subscribe button is now consistently styled and not a complete block button anymore. approved by @awhildy

Screenshots (if relevant)

before:

after:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #24281 (closed)

app/assets/javascripts/boards/components/board_sidebar.js.es6

@@ -47,7 +47,7 @@
       new gl.DueDateSelectors();
       new LabelsSelect();
       new Sidebar();
-      new Subscription('.subscription');
+      gl.Subscription.bindAll('.subscription');
     }
   });
 })();