don't specify a chromedriver version in example yml

after g/255045, we don't need to override the version jenkins uses
to do local selenium testing anymore, so simply removing the line
saves the trouble of updating it every time there's a new version
of chrome

test plan:
 - remove chromedriver_version from config/selenium.yml
 - you should be able to run selenium specs locally

Change-Id: Ia2ccd9fbe6ed518adbcc9c6cf0755e4e22f4507a
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/279761
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: James Butters <jbutters@instructure.com>
QA-Review: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>

config/selenium.yml.example

@@ -1,7 +1,7 @@
 test:
   host: "localhost"
   browser: "chrome"
-  chromedriver_version: "94.0.4606.61"
+  # chromedriver_version: "94.0.4606.61"
   # auto_open_devtools: true
   # headless: true
   # window_size: "1237,974"