Update CONTRIBUTING.md (#838)

/vote

### Feature or Bugfix
- Refactoring

### Detail
- Removing the statement that says we might ask contributors to sign a
Contributor Licence Agreement and replacing with a simple statement that
says all contributions will be made in accordance with the LICENCE.txt
file.

### Relates
- N/A

### Security
Please answer the questions below briefly where applicable, or write
`N/A`. Based on
[OWASP 10](https://owasp.org/Top10/en/).

- Does this PR introduce or modify any input fields or queries - this
includes
fetching data from storage outside the application (e.g. a database, an
S3 bucket)? N/A
  - Is the input sanitized? N/A
- What precautions are you taking before deserializing the data you
consume? N/A
  - Is injection prevented by parametrizing queries? N/A
  - Have you ensured no `eval` or similar functions are used? N/A
- Does this PR introduce any functionality or component that requires
authorization? N/A
- How have you ensured it respects the existing AuthN/AuthZ mechanisms?
N/A
  - Are you logging failed auth attempts? N/A
- Are you using or adding any cryptographic features? N/A
  - Do you use a standard proven implementations? N/A
- Are the used keys controlled by the customer? Where are they stored?
N/A
- Are you introducing any new policies/roles/users? N/A
  - Have you used the least-privilege principle? How? N/A


By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

CONTRIBUTING.md

@@ -68,6 +68,4 @@ If you discover a potential security issue in this project we ask that you notif
 
 ## Licensing
 
-See the [LICENSE](./LICENCE.txt) file for our project's licensing. We will ask you to confirm the licensing of your contribution.
-
-We may ask you to sign a [Contributor License Agreement (CLA)](http://en.wikipedia.org/wiki/Contributor_License_Agreement) for larger changes.
+See the [LICENSE](./LICENCE.txt) file for our project's licensing. By submitting a contribution, you agree that your contribution will be licensed in accordance with the LICENSE file.