docs: sysctl/fs: merge the aio sections

There are two sections documenting aio-nr and aio-max-nr, merge them.
I kept the second explanation of aio-nr, which seems clearer to me,
along with the effects of the values from the first section.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20220930102937.135841-4-steve@sk2.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/sysctl/fs.rst

@@ -50,11 +50,11 @@ Currently, these files are in /proc/sys/fs:
 aio-nr & aio-max-nr
 -------------------
 
-aio-nr is the running total of the number of events specified on the
-io_setup system call for all currently active aio contexts.  If aio-nr
-reaches aio-max-nr then io_setup will fail with EAGAIN.  Note that
-raising aio-max-nr does not result in the pre-allocation or re-sizing
-of any kernel data structures.
+aio-nr shows the current system-wide number of asynchronous io
+requests.  aio-max-nr allows you to change the maximum value
+aio-nr can grow to.  If aio-nr reaches aio-nr-max then io_setup will
+fail with EAGAIN.  Note that raising aio-max-nr does not result in the
+pre-allocation or re-sizing of any kernel data structures.
 
 
 dentry-state
@@ -287,14 +287,6 @@ mount more filesystems than the current value in super-max
 allows you to.
 
 
-aio-nr & aio-max-nr
--------------------
-
-aio-nr shows the current system-wide number of asynchronous io
-requests.  aio-max-nr allows you to change the maximum value
-aio-nr can grow to.
-
-
 mount-max
 ---------