Remove mentions of ENOSYS added in d97e44784b

aio(4) is a hard requirement in the kernel as of f3215338ef. The
scenario that the patch was submitted for is no longer possible.

This isn't a straight up revert since the previous change also addressed
some minor issues.

PR:		190942
Reported by:	asomers
MFC after:	2 weeks
MFC with:	d97e44784b
Fixes:		d97e44784b ("aio_*(2): mention ENOSYS under ERRORS")
Differential Revision: https://reviews.freebsd.org/D49541

lib/libsys/aio_cancel.2

@@ -80,13 +80,6 @@ The
 .Fa fildes
 argument
 is an invalid file descriptor.
-.It Bq Er ENOSYS
-The
-.Fn aio_cancel
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_error 2 ,

lib/libsys/aio_error.2

@@ -72,13 +72,6 @@ The
 .Fa iocb
 argument
 does not reference an outstanding asynchronous I/O request.
-.It Bq Er ENOSYS
-The
-.Fn aio_error
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_cancel 2 ,

lib/libsys/aio_fsync.2

@@ -136,13 +136,6 @@ argument
 is not a valid descriptor.
 .It Bq Er EINVAL
 This implementation does not support synchronized I/O for this file.
-.It Bq Er ENOSYS
-The
-.Fn aio_fsync
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .El
 .Pp
 If the request is successfully enqueued, but subsequently cancelled

lib/libsys/aio_mlock.2

@@ -98,13 +98,6 @@ The request was not queued because of system resource limitations.
 The asynchronous notification method in
 .Fa iocb->aio_sigevent.sigev_notify
 is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_mlock
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .El
 .Pp
 If the request is successfully enqueued, but subsequently cancelled

lib/libsys/aio_read.2

@@ -173,13 +173,6 @@ points outside the process's allocated address space.
 The asynchronous notification method in
 .Fa iocb->aio_sigevent.sigev_notify
 is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_read
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .It Bq Er EOPNOTSUPP
 Asynchronous read operations on the file descriptor
 .Fa iocb->aio_fildes

lib/libsys/aio_return.2

@@ -79,13 +79,6 @@ The I/O operation was submitted with
 and the value of the
 .Fa aio_lio_opcode
 is invalid.
-.It Bq Er ENOSYS
-The
-.Fn aio_return
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_cancel 2 ,

lib/libsys/aio_suspend.2

@@ -89,13 +89,6 @@ contains more asynchronous I/O requests than the
 variable, or at least one of the requests is not valid.
 .It Bq Er EINTR
 the suspend was interrupted by a signal.
-.It Bq Er ENOSYS
-The
-.Fn aio_suspend
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .El
 .Sh SEE ALSO
 .Xr aio_cancel 2 ,

lib/libsys/aio_waitcomplete.2

@@ -101,13 +101,6 @@ A signal was delivered before the timeout expired and before any
 asynchronous I/O requests completed.
 .It Bq Er EINVAL
 The specified time limit is invalid.
-.It Bq Er ENOSYS
-The
-.Fn aio_waitcomplete
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .It Bq Er EWOULDBLOCK
 .It Bq Er EINPROGRESS
 The specified time limit expired before any asynchronous I/O requests

lib/libsys/aio_write.2

@@ -182,13 +182,6 @@ points outside the process's allocated address space.
 The asynchronous notification method in
 .Fa iocb->aio_sigevent.sigev_notify
 is invalid or not supported.
-.It Bq Er ENOSYS
-The
-.Fn aio_write
-system call is not supported.
-This can occur if
-.Xr aio 4
-support is not present.
 .It Bq Er EOPNOTSUPP
 Asynchronous write operations on the file descriptor
 .Fa iocb->aio_fildes