Docs: Remove the CLA checkbox in the pull request template

Docs: Remove the CLA checkbox in the pull request template

The EasyCLA status check is required so this won't get missed. The old JSF CLA
is dead, the provided link doesn't return meaningful information. There's no
good replacement link for the old CLA; PR authors are just supposed to sign the
new CLA by clicking on a link posted by the EasyCLA bot when they submit their
first PR since EasyCLA was enabled for the repo.

Closes gh-4937

(cherry picked from commit e124893132d7a979d7987f978e968a1f889348b6)