[keyserver] Remove target blank

Summary: Unfortunately, it doesn't solve https://linear.app/comm/issue/ENG-4089/invite-links-dont-work-on-prod.

Test Plan: Check if clicking a link in Chrome doesn't open a new card.

Reviewers: kamil, inka

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8486

keyserver/src/responders/website-responders.js

@@ -801,11 +801,7 @@ async function inviteResponder(req: $Request, res: $Response): Promise<void> {
           <div class="separator"></div>
           <section class="buttons">
             <a class="button" href="${stores.appStoreUrl}">Download Comm</a>
-            <a
-              class="button secondary"
-              href="${inviteLinkUrl(secret)}"
-              target="_blank"
-            >
+            <a class="button secondary" href="${inviteLinkUrl(secret)}">
               Invite Link
             </a>
           </section>