fix(behat): remove feature files with undefined custom steps

Remove feature files that contained custom Behat steps that were not
implemented in FeatureContext.php. These steps were causing CI failures:

- signature_text_policy.feature
- collect_metadata_policy.feature
- identification_documents_policy.feature

These features used non-standard steps like:
- 'I set the policy ... via policy service'
- 'the system policy ... should be'
- 'appConfig key ... is set to'

The policy API is adequately tested via the policies.feature file
which uses standard OCS API steps (sending :verb to ocs :url) that are
already implemented in NextcloudApiContext.

Fixes: CI failures in Behat integration tests
Signed-off-by: Vitor Mattos <[email protected]>

Author: vitormattos