clean(core): remove unused package in the previewable interface

Author: ThibaultBee

core/src/main/java/io/github/thibaultbee/streampack/core/elements/sources/video/IPreviewableSource.kt

@@ -21,7 +21,6 @@ import android.view.SurfaceHolder
 import android.view.SurfaceView
 import android.view.TextureView
 import io.github.thibaultbee.streampack.core.interfaces.setPreview
-import io.github.thibaultbee.streampack.core.interfaces.startPreview
 import io.github.thibaultbee.streampack.core.streamers.single.SingleStreamer
 import kotlinx.coroutines.flow.StateFlow