Hide Delete Backup button when Secure Backup required

If Secure Backup is required by the HS admin, then this hides the Delete Backup
button in Settings to ensure everyone keeps their backup per policy.

Part of https://github.com/vector-im/element-web/issues/14954

src/components/views/settings/KeyBackupPanel.js

@@ -21,6 +21,7 @@ import * as sdk from '../../../index';
 import {MatrixClientPeg} from '../../../MatrixClientPeg';
 import { _t } from '../../../languageHandler';
 import Modal from '../../../Modal';
+import { isSecureBackupRequired } from '../../../utils/WellKnownUtils';
 
 export default class KeyBackupPanel extends React.PureComponent {
     constructor(props) {
@@ -315,14 +316,19 @@ export default class KeyBackupPanel extends React.PureComponent {
                 trustedLocally = _t("This backup is trusted because it has been restored on this session");
             }
 
+            let deleteBackupButton;
+            if (!isSecureBackupRequired()) {
+                deleteBackupButton = <AccessibleButton kind="danger" onClick={this._deleteBackup}>
+                    {_t("Delete Backup")}
+                </AccessibleButton>;
+            }
+
             const buttonRow = (
                 <div className="mx_KeyBackupPanel_buttonRow">
                     <AccessibleButton kind="primary" onClick={this._restoreBackup}>
                         {restoreButtonCaption}
                     </AccessibleButton>&nbsp;&nbsp;&nbsp;
-                    <AccessibleButton kind="danger" onClick={this._deleteBackup}>
+                    {deleteBackupButton}
-                        {_t("Delete Backup")}
-                    </AccessibleButton>
                 </div>
             );