[2/N] Move Legacy only methods calls to OomAdjusterLegacyImpl

Only the OomAdjusterLegacyImpl uses `updateOomAdjInnerLSP` (which is the
common update logic for all three update entry points).

Flag: EXEMPT pure refactor
Test: atest MockingOomAdjusterTests
Test: builds and flashes
Bug: 306731120
Change-Id: I2da062858a2b8efc5b7ab332520ae281bfe9eca6