Fix comment "add" buttons being hidden in StreamField

client/src/components/StreamField/blocks/FieldBlock.js

@@ -78,7 +78,6 @@ export class FieldBlock {
       addCommentButtonElement.classList.add(
         'w-field__comment-button',
         'w-field__comment-button--add',
-        'u-hidden',
       );
 
       ReactDOM.render(

client/src/components/StreamField/blocks/__snapshots__/FieldBlock.test.js.snap

@@ -51,7 +51,7 @@ exports[`telepath: wagtail.blocks.FieldBlock with comments enabled it renders co
           <div class=\\"w-field__help\\" id=\\"the-prefix-helptext\\" data-field-help=\\"\\"><p class=\\"help\\">drink <em>more</em> water</p></div>
           <div class=\\"w-field__input\\" data-field-input=\\"\\">
             <p name=\\"the-prefix\\" id=\\"the-prefix\\">The widget</p>
-          <button type=\\"button\\" aria-label=\\"Add Comment\\" data-comment-add=\\"\\" class=\\"w-field__comment-button w-field__comment-button--add u-hidden\\"><svg class=\\"icon icon-comment-add \\" aria-hidden=\\"true\\"><use href=\\"#icon-comment-add\\"></use></svg><svg class=\\"icon icon-comment-add-reversed \\" aria-hidden=\\"true\\"><use href=\\"#icon-comment-add-reversed\\"></use></svg></button></div>
+          <button type=\\"button\\" aria-label=\\"Add Comment\\" data-comment-add=\\"\\" class=\\"w-field__comment-button w-field__comment-button--add\\"><svg class=\\"icon icon-comment-add \\" aria-hidden=\\"true\\"><use href=\\"#icon-comment-add\\"></use></svg><svg class=\\"icon icon-comment-add-reversed \\" aria-hidden=\\"true\\"><use href=\\"#icon-comment-add-reversed\\"></use></svg></button></div>
         </div>
       </div>"
 `;