Remove Google-internal link from URL display guidelines

TBR=meacer@chromium.org

Change-Id: I3dd17ffa9f60e4efc07bee69d92ef7f5783097e7
Reviewed-on: https://chromium-review.googlesource.com/c/1407109
Commit-Queue: Emily Stark <estark@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622022}

docs/security/url_display_guidelines/url_display_guidelines.md

@@ -101,7 +101,7 @@ Do not attempt to write your own canonicalizer.
 
     * Omit default ports (80 for http, 443 for https).
 
-    * If in a space-constrained environment, it's acceptable to use registrable domain instead of the full origin. (e.g., [AMP for CCT](https://docs.google.com/presentation/d/1SNAvoQdXvQsYJAdMJbdCaRvzP3fUYKS87dknrHDV4xU/edit#slide=id.p))
+    * If in a space-constrained environment, it's acceptable to use registrable domain instead of the full origin.
 
 ### Eliding URLs