Remove test case for deprecated policy EnableDeprecatedWebPlatformFeatures.

BUG=1121162
TBR=pastarmovj@chromium.org
NOTRY=true

Change-Id: I2b19fff83f5a8372504854f93c2fd1221afdbba4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444311
Commit-Queue: Greg Thompson <grt@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813095}

chrome/test/data/policy/policy_test_cases.json

@@ -4721,8 +4721,7 @@
   },
 
   "EnableDeprecatedWebPlatformFeatures": {
-    "os": ["win", "linux", "mac", "chromeos"],
-    "policy_pref_mapping_test": []
+    "note": "This policy has been removed, as of M88."
   },
 
   "TouchVirtualKeyboardEnabled": {