Update documentation for how to disable WPT auto-import

The previously linked CL no longer applies, and can't be landed
directly or cherry-picked.

Bug: 1032951
Change-Id: Ib325c2c1f84fd17813421d32f1aa4174e496e973
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1960349
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#723940}

docs/testing/web_platform_tests.md

@@ -48,8 +48,8 @@ For maintainers:
 
 -   The source lives in
     [third_party/blink/tools/wpt_import.py](../../third_party/blink/tools/wpt_import.py).
--   If the importer starts misbehaving, it could be disabled by turning off the
-    auto-import mode by landing [this CL](https://crrev.com/c/617479/).
+-   If the importer starts misbehaving, it can be disabled by landing a
+    [CL to skip the update step](https://crrev.com/c/1961906/).
 
 ### Failures caused by automatic imports.