Adds old API to StatsManager (temporary need).

We changed the API to use long-based config keys instead of strings,
but we have some code that depends on the old API. Let's add them
back temporarily. The old API (that does nothing now) will be
deleted next month.

Test: N/A. Just to prevent build failures.
Bug: 69522276
Change-Id: Ibc51622371d4f3ced3e9b2f66a862dea1ac1c63c