Bug 1701365 - Set buttonpack to end in markup r=mconley

Removed js code that set buttonpack to "end" and modified markup to do that instead.

Differential Revision: https://phabricator.services.mozilla.com/D117935

toolkit/components/prompts/content/commonDialog.js

@@ -66,7 +66,6 @@ function commonDialogOnLoad() {
   if (args.headerIconURL) {
     root.style.setProperty("--icon-url", `url('${args.headerIconURL}')`);
   }
-  dialog.setAttribute("buttonpack", "end");
   // Fade and crop potentially long raw titles, e.g., origins and hostnames.
   title.shouldUseMaskFade = title.raw && (args.authOrigin || promptPrincipal);
   root.setAttribute("headertitle", JSON.stringify(title));

toolkit/components/prompts/content/commonDialog.xhtml

@@ -18,7 +18,7 @@
         headerparent="dialogGrid"
         onunload="commonDialogOnUnload();">
 <dialog id="commonDialog"
-        buttonpack="center">
+        buttonpack="end">
 
   <linkset>
     <html:link rel="localization" href="branding/brand.ftl"/>