Don't include metrics.js on enterprise builds.

It throws an exception when the mixpanel library is not present. This
exception breaks emoji autocomplete, among other things.

(imported from commit 6ae2a69d40282701b8717b60d887836416c85a6c)

zproject/settings.py

@@ -513,7 +513,6 @@ JS_SPECS = {
             'js/avatar.js',
             'js/settings.js',
             'js/tab_bar.js',
-            'js/metrics.js',
             'js/emoji.js',
             'js/referral.js'
         ],
@@ -532,13 +531,18 @@ JS_SPECS = {
     },
 }
 
+app_srcs = JS_SPECS['app']['source_filenames']
+
 if not DEBUG:
     # This file is generated by update-prod-static.
     # In dev we fetch individual templates using Ajax.
-    app_srcs = JS_SPECS['app']['source_filenames']
     app_srcs.insert(app_srcs.index('third/handlebars/handlebars.runtime.js') + 1,
                     'templates/compiled.js')
 
+if MIXPANEL_TOKEN:
+    # Mixpanel is not used on enterprise and throws an error when the
+    # library is not included
+    app_srcs.append('js/metrics.js')
 
 PIPELINE_JS = {}  # Now handled in tools/minify-js
 PIPELINE_JS_COMPRESSOR  = None