ART: Remove assert include (iwyu)

casts.h does not actually use assert anymore.

Test: mmma art
Change-Id: If73095d50d91289c974110eb707b3b33932bed98
diff --git a/libartbase/base/casts.h b/libartbase/base/casts.h
index 76ff679..cedd624 100644
--- a/libartbase/base/casts.h
+++ b/libartbase/base/casts.h
@@ -17,7 +17,6 @@
 #ifndef ART_LIBARTBASE_BASE_CASTS_H_
 #define ART_LIBARTBASE_BASE_CASTS_H_
 
-#include <assert.h>
 #include <stdint.h>
 #include <string.h>