Remove duplicate typedef of AESContext.

Pavel Kryukov points out that ssh.h has this typedef, so sshaes.c
doesn't have to have it too, and in C89 mode it's an error to have it
twice.

sshaes.c

@@ -48,8 +48,6 @@
 #    define INLINE
 #endif
 
-typedef struct AESContext AESContext;
-
 struct AESContext {
     word32 keysched_buf[(MAX_NR + 1) * NB + 3];
     word32 invkeysched_buf[(MAX_NR + 1) * NB + 3];