chore(os-login): rm unused config API path (#12858)

Removing unused API path from config for os-login, so that it matches
the generated code status.

v1beta of java-os-login was added to the generation_config.yaml as part
of initial migration to hermetic build:
14b7346,
but client library code for v1beta is not present in
java-os-login/google-cloud-os-login dir. This is due to deep-copy-regex
being too strict and does not copy /v1beta from staging dir to final
output.

Expect generation workflow to run successfully with not change. (no
sample code exists for
[os-login](https://github.com/googleapis/google-cloud-java/tree/main/java-os-login))

For #12736
For googleapis/librarian#5370

Author: zhumin8

generation_config.yaml

@@ -1976,7 +1976,6 @@ libraries:
   issue_tracker: https://issuetracker.google.com/savedsearches/559755
   GAPICs:
   - proto_path: google/cloud/oslogin/v1
-  - proto_path: google/cloud/oslogin/v1beta
 - api_shortname: parallelstore
   name_pretty: Parallelstore API
   product_documentation: https://cloud/parallelstore?hl=en