Update banner with two weeks left for early bird pricing(#1451)

Author: cjqzhao

layouts/partials/banner.html

@@ -1,15 +1,10 @@
 {{ if site.Params.show_banner -}}
 <div class="o-banner">
   <p>
-    gRPConf 2025 is on <strong>Aug. 26th!</strong> -
+    Only two more weeks until July 30th to get Early Bird tickets ($50) for gRPConf 2025 on <strong>Aug. 26th!</strong> -
     <a href="https://events.linuxfoundation.org/grpconf/" target="_blank" rel="noopener">
       <strong>Register now</strong>
     </a>
-    ($50 until Jul 30th) or
-    <a href="https://events.linuxfoundation.org/grpconf/program/cfp/" target="_blank" rel="noopener">
-      <strong>Submit a talk proposal</strong>
-    </a>
-    (by May 28th)
   </p>
 </div>
 {{ end -}}