remove selenium from Jenkinsfile.docker-sync
remove selenium from Jenkinsfile.docker-sync

the proper place to update the version of selenium is in
Jenkinsfile.selenium-chrome using
docker-compose/selenium-chrome/Dockerfile

Change-Id: I1c4b76f91229ed6fbced8a4042a743a371511a96
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/284975
Reviewed-by: Andrea Cirulli <b4e55ef5ee4bae8ad31f7c81009bfc0af1714a1f@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>
Product-Review: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms