Restore caching for License.current logic

What does this MR do and why?

We currently have some failures in the E2E tests which showed up after introducing some strong memoization and caching changes to the license model in !99757 (merged). An initial attempt to fix the failures by removing the caching on some instance methods again in https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/2672 still resulted in the E2E failures.

This will remove the other modifications on the License model by removing the strong memoize for License.current and use the caching mechanism again.

MR acceptance checklist

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