drm_hwcomposer: remove compositor interface

The compositor interface had only one implementation and one user. The
compositor interface also needs to change to accomodate some changes for
fences to work optimally.

Change-Id: I02d21b0a0e86fa21b3c5f4ad84ff571611643994
diff --git a/drmresources.cpp b/drmresources.cpp
index 9be990f..feb5187 100644
--- a/drmresources.cpp
+++ b/drmresources.cpp
@@ -467,7 +467,7 @@
     return -EINVAL;
   }
 
-  DrmComposition *comp = (DrmComposition *)compositor_.CreateComposition(NULL);
+  DrmComposition *comp = compositor_.CreateComposition(NULL);
   if (!comp) {
     ALOGE("Failed to create composition for dpms on %d", display);
     return -ENOMEM;
@@ -478,7 +478,7 @@
     delete comp;
     return ret;
   }
-  ret = compositor_.QueueComposition((Composition *)comp);
+  ret = compositor_.QueueComposition(comp);
   if (ret) {
     ALOGE("Failed to queue dpms composition on %d %d", display, ret);
     return ret;