defer persona init till after people launch the login dialog

app/views/common/_persona_javascript.html.erb

@@ -1,29 +0,0 @@
-<!-- TODO, move this into login UI, don't deliver with page -->
-<script>
-  $LAB.script("https://login.persona.org/include.js").wait(function(){
-  (function() {
-    var readyCalled = false;
-    navigator.id.watch({
-      onlogin: function(assertion) {
-        if (readyCalled) {
-          Discourse.ajax('/auth/persona/callback', {
-            type: 'POST',
-            data: { 'assertion': assertion },
-            dataType: 'json'
-          }).then(function(data) {
-            Discourse.authenticationComplete(data);
-          });
-        }
-      },
-      onlogout: function() {
-        if (readyCalled) {
-          Discourse.logout();
-        }
-      },
-      onready: function() {
-        readyCalled = true;
-      }
-    });
-  }());
-  });
-</script>