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
Merged-In: I344f46b65b5c473930b16b9b4041e4897384dc18