Remove the "all" channel

The "all" channel fundamentally doesn't scale, because it needs
to fetch N builds from the database (where N is potentially a very
large number), then check whether they are still valid.  And it's
not very useful anyway.

src/root/jobset.tt

@@ -221,7 +221,7 @@
 		
 			<h2>Channels</h2>
 			
-			<p>This jobset provides the following Nix channels:</p>
+			<p>This jobset provides the following Nix channel:</p>
 			
 			<ul>
 			  <li>
@@ -229,11 +229,6 @@
 			    'latest') %]"><tt>latest</tt></a> — contains the latest successful
 			    build of every job in this jobset.
 			  </li>
-			  <li>
-			    <a href="[% c.uri_for('/jobset' project.name jobset.name 'channel'
-			    'all') %]"><tt>all</tt></a> — contains every successful,
-			    non-garbage-collected build of every job in this project.
-			  </li>
 			</ul>
 			
 		</div>