mk-ca-bundle: Remove URL for aurora

Aurora is no longer used by Mozilla
https://hacks.mozilla.org/2017/04/simplifying-firefox-release-channels/
diff --git a/lib/mk-ca-bundle.pl b/lib/mk-ca-bundle.pl
index d16f1a4..dcfec0b 100755
--- a/lib/mk-ca-bundle.pl
+++ b/lib/mk-ca-bundle.pl
@@ -50,8 +50,6 @@
     'https://hg.mozilla.org/projects/nss/raw-file/default/lib/ckfw/builtins/certdata.txt',
   'central' =>
     'https://hg.mozilla.org/mozilla-central/raw-file/default/security/nss/lib/ckfw/builtins/certdata.txt',
-  'aurora' =>
-    'https://hg.mozilla.org/releases/mozilla-aurora/raw-file/default/security/nss/lib/ckfw/builtins/certdata.txt',
   'beta' =>
     'https://hg.mozilla.org/releases/mozilla-beta/raw-file/default/security/nss/lib/ckfw/builtins/certdata.txt',
   'release' =>