io_uring: remove io_uring_cqwait_reg_arg

A separate wait argument registration API was removed, also delete
leftover uapi definitions.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/143b6a53591badac23632d3e6fa3e5db4b342ee2.1731942445.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

include/uapi/linux/io_uring.h

@@ -873,20 +873,6 @@ enum {
 	IORING_REG_WAIT_TS		= (1U << 0),
 };
 
-/*
- * Argument for IORING_REGISTER_CQWAIT_REG, registering a region of
- * struct io_uring_reg_wait that can be indexed when io_uring_enter(2) is
- * called rather than pass in a wait argument structure separately.
- */
-struct io_uring_cqwait_reg_arg {
-	__u32		flags;
-	__u32		struct_size;
-	__u32		nr_entries;
-	__u32		pad;
-	__u64		user_addr;
-	__u64		pad2[3];
-};
-
 /*
  * Argument for io_uring_enter(2) with
  * IORING_GETEVENTS | IORING_ENTER_EXT_ARG_REG set, where the actual argument