README: Remove outdated CLA link

[reuterbal]

CLA is automatically being linked via PR template.

Description

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[awnawab]

Thanks a lot for this @reuterbal 🙏 I'll merge once the CI is green and my ocd is satisfied.