Remove unused includes and forward declarations in libmediaextractor/include

Test: make checkbuild
Bug: 67908556
Change-Id: If840305af5c043bb8014590eb208cf11c99e61ee
diff --git a/media/libmediaplayerservice/nuplayer/GenericSource.h b/media/libmediaplayerservice/nuplayer/GenericSource.h
index 856f03b..2406665 100644
--- a/media/libmediaplayerservice/nuplayer/GenericSource.h
+++ b/media/libmediaplayerservice/nuplayer/GenericSource.h
@@ -35,6 +35,7 @@
 class IDataSource;
 struct IMediaHTTPService;
 struct MediaSource;
+class IMediaSource;
 class MediaBuffer;
 struct MediaClock;
 struct NuCachedSource2;