Bug 1821920 - Remove redundant <hbox> in privacy settings. r=Gijs,settings-reviewers

Bug 1822131 will improve the situation here, but meanwhile this fixes the issue
by removing a redundant horizontal box.

Differential Revision: https://phabricator.services.mozilla.com/D172455

browser/components/preferences/privacy.inc.xhtml

@@ -112,9 +112,7 @@
                 </hbox>
               </vbox>
               <vbox id="etpStandardTCPBox" class="content-blocking-warning info-box-container">
-                <hbox>
-                  <label class="content-blocking-warning-title" data-l10n-id="content-blocking-etp-standard-tcp-title"/>
-                </hbox>
+                <label class="content-blocking-warning-title" data-l10n-id="content-blocking-etp-standard-tcp-title"/>
                 <description>
                   <html:span class="tail-with-learn-more" data-l10n-id="content-blocking-etp-standard-tcp-rollout-description"></html:span>
                   <html:a is="moz-support-link"