Remove mentions of ENOSYS added in d97e44784bb5

[ngie]

Summary

aio(4) is a hard requirement in the kernel as of f3215338ef82. 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.

MFC after: 2 weeks
Fixes: d97e44784bb5 ("aio_*(2): mention ENOSYS under ERRORS")
Reported by: asomers
PR: 190942

Test Plan

Confirmed the net change to the manpages:

% git diff d97e44784bb5a510b7af7593c86cfbcff73855c4^.. aio_*
diff --git a/lib/libsys/aio_read.2 b/lib/libsys/aio_read.2
index 3a9601754c06..f7d8cdfd71b1 100644
--- a/lib/libsys/aio_read.2
+++ b/lib/libsys/aio_read.2
@@ -263,7 +263,9 @@ The
 .Fn aio_read2
 and
 .Fn aio_readv
-system calls are FreeBSD extensions,
+system calls are
+.Fx
+extensions,
 and should not be used in portable code.
 .Sh HISTORY
 The
diff --git a/lib/libsys/aio_waitcomplete.2 b/lib/libsys/aio_waitcomplete.2
index 1f20eca942ab..f14e05abaaf0 100644
--- a/lib/libsys/aio_waitcomplete.2
+++ b/lib/libsys/aio_waitcomplete.2
@@ -91,8 +91,6 @@ The
 .Fn aio_waitcomplete
 system call fails if:
 .Bl -tag -width Er
-.It Bq Er EINVAL
-The specified time limit is invalid.
 .It Bq Er EAGAIN
 The process has not yet called
 .Fn aio_read
@@ -101,6 +99,8 @@ or
 .It Bq Er EINTR
 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 EWOULDBLOCK
 .It Bq Er EINPROGRESS
 The specified time limit expired before any asynchronous I/O requests
diff --git a/lib/libsys/aio_write.2 b/lib/libsys/aio_write.2
index f59406b8ab36..875b24fa160a 100644
--- a/lib/libsys/aio_write.2
+++ b/lib/libsys/aio_write.2
@@ -265,7 +265,9 @@ The
 .Fn aio_write2
 and
 .Fn aio_writev
-system calls are FreeBSD extensions,
+system calls are
+.Fx
+extensions,
 and should not be used in portable code.
 .Sh HISTORY
 The

I never bumped .Dd since I got distracted earlier with other work...