ENSCORESW-2903: remove possible null analysis_id from unique key

Created by: magaliruffier

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion;
• Review the contributing guidelines for this repository; remember in particular:
  • do not modify code without testing for regression
  • provide simple unit tests to test the changes
  • if you change the schema you must patch the test databases as well, see Updating the schema
  • the PR must not fail unit testing

Description

Using one or more sentences, describe in detail the proposed changes. Patch is for release 95 but was only added to master, porting this back to release/95 branch

Use case

Describe the problem. Please provide an example representing the motivation behind the need for having these changes in place. Schema for 95 is correct and reflects what is available in the databases for 95 Initial pull request is available here: https://github.com/Ensembl/ensembl/pull/319

Benefits

If applicable, describe the advantages the changes will have. Schema for 95 is correct and reflects what is available in the databases for 95

Possible Drawbacks

If applicable, describe any possible undesirable consequence of the changes.

Testing

Have you added/modified unit tests to test the changes? NA

If so, do the tests pass/fail? NA

Have you run the entire test suite and no regression was detected? Yes