drm_hwcomposer: Remove DrmCompositionRegion struct

The structure is currently unused.

Signed-off-by: Matvii Zorin <matvii.zorin@globallogic.com>
diff --git a/compositor/DrmDisplayComposition.h b/compositor/DrmDisplayComposition.h
index 3a10a8c..d7ee9cf 100644
--- a/compositor/DrmDisplayComposition.h
+++ b/compositor/DrmDisplayComposition.h
@@ -50,10 +50,6 @@
       default;
 };
 
-struct DrmCompositionRegion {
-  std::vector<size_t> source_layers;
-};
-
 class DrmCompositionPlane {
  public:
   enum class Type : int32_t {