doc/rados/ops: edit cache-tiering.rst

Remove part of a sentence that might have led readers to think that it
is a good idea to deploy cache tiering on releases prior to Reef.

This incorporates Anthony D'Atri's suggestion from here: ceph#63614 (comment)

Signed-off-by: Zac Dover <[email protected]>
(cherry picked from commit 3618b1b)

Author: zdover23

doc/rados/operations/cache-tiering.rst

@@ -8,7 +8,7 @@
    notice.
 
    The upstream Ceph community strongly advises against deploying new cache
-   tiers to releases after the Reef release.
+   tiers.
 
 A cache tier provides Ceph Clients with better I/O performance for a subset of
 the data stored in a backing storage tier. Cache tiering involves creating a