Remove DrmInitialization from IDataSource

DrmInitialization only needs to be called on PlayerServiceFileSource
and PlayerServiceMediaHTTP, so just have those initialize the forward
lock engine automatically, which removes the need to have this in the
IDataSource interface.

Test: atest cts/tests/tests/drm/src/android/drm/cts/DRMTest.java

Change-Id: I344f46b65b5c473930b16b9b4041e4897384dc18