drm_hwcomposer: Purge drm_ from drmdisplaycompositor

Having DrmDevice as a member in DrmDisplayCompositor is redundant,
since that could be always retrieved by calling:
resource_manager_->GetDrmDevice(display_)

Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
diff --git a/drmdisplaycompositor.h b/drmdisplaycompositor.h
index 6212597..bc13d4c 100644
--- a/drmdisplaycompositor.h
+++ b/drmdisplaycompositor.h
@@ -41,7 +41,7 @@
   DrmDisplayCompositor();
   ~DrmDisplayCompositor();
 
-  int Init(ResourceManager *resource_manager, DrmDevice *drm, int display);
+  int Init(ResourceManager *resource_manager, int display);
 
   std::unique_ptr<DrmDisplayComposition> CreateComposition() const;
   int ApplyComposition(std::unique_ptr<DrmDisplayComposition> composition);
@@ -80,7 +80,6 @@
   std::tuple<int, uint32_t> CreateModeBlob(const DrmMode &mode);
 
   ResourceManager *resource_manager_;
-  DrmDevice *drm_;
   int display_;
 
   std::unique_ptr<DrmDisplayComposition> active_composition_;