aomdx.h: remove circular aom_decrypt_init typedef

BUG=aomedia:111

Change-Id: I4e18705a36227e23f9ead51ef98a7bad51c998d4

aom/aomdx.h

diff --git a/aom/aomdx.h b/aom/aomdx.h
index 19256fb..834cdff 100644
--- a/aom/aomdx.h
+++ b/aom/aomdx.h
@@ -145,10 +145,6 @@
   void *decrypt_state;
 } aom_decrypt_init;
 
-/*!\brief A deprecated alias for aom_decrypt_init.
- */
-typedef aom_decrypt_init aom_decrypt_init;
-
 /*!\cond */
 /*!\brief AOM decoder control function parameter type
  *