Remove Chromium-specific file path in WPT feature policy README

A Chromium-specific path was introduced in crrev.com/c/571019 and
made it upstream. This removes the sentence containing the path.

Bug:
Change-Id: I16a89ae2e9b321a8d5bfbcbb2dc4488636dc242b
Reviewed-on: https://chromium-review.googlesource.com/603917
Reviewed-by: Luna Lu <loonybear@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Jeff Carpenter <jeffcarp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#497505}

feature-policy/README.md

@@ -1,9 +1,7 @@
 # Feature Policy Guide
 ## How to Test a New Feature with Feature Policy
 
-This directory contains a framework to test features with feature policy. Please
-refer to `/content/common/feature_policy/README.md` for more details on feature
-policy.
+This directory contains a framework to test features with feature policy.
 
 When adding a new feature to feature policy, the following cases should be tested:
 * feature enabled by header policy [HTTP tests]