remove arch-specific bits/ipc.h that are identical to generic

previously these differed from generic because they needed their own
definitions of IPC_64. now that it's no longer in public header,
they're identical.

arch/or1k/bits/ipc.h

-struct ipc_perm {
-	key_t __ipc_perm_key;
-	uid_t uid;
-	gid_t gid;
-	uid_t cuid;
-	gid_t cgid;
-	mode_t mode;
-	int __ipc_perm_seq;
-	long __pad1;
-	long __pad2;
-};

arch/x86_64/bits/ipc.h

-struct ipc_perm {
-	key_t __ipc_perm_key;
-	uid_t uid;
-	gid_t gid;
-	uid_t cuid;
-	gid_t cgid;
-	mode_t mode;
-	int __ipc_perm_seq;
-	long __pad1;
-	long __pad2;
-};