[chromedriver] Remove deprecated extension section

Automation extension is no longer needed or supported since 85

Change-Id: I6a57f8efd99cec3cde2b2a6de431f8612169b23c
Bug: chromedriver:3376
no-try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2579881Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Shengfa Lin <shengfa@google.com>
Cr-Commit-Position: refs/heads/master@{#834982}

chrome/test/chromedriver/README.md

@@ -101,9 +101,6 @@ Code for a python client.
 Code for the chromedriver server.
 A python wrapper to the chromedriver server.
 
-* [extension/](extension/):
-An extension used for automating the desktop browser.
-
 * [test/](test/):
 Integration tests.