[cat] Remove outdated comment in aarch64fences.cat

Signed-off-by: Nikos Nikoleris <[email protected]>

herd/libdir/aarch64fences.cat

@@ -53,9 +53,9 @@ let dsb.ld = DSB.ISHLD | DSB.OSHLD | DSB.LD
 let dsb.st = DSB.ISHST | DSB.OSHST | DSB.ST
 
 (*
- * A further restriction is that standard litmus tests are unable to
- * distinguish between DMB and DSB instructions, so the model treats
- * them as equivalent to each other.
+ * A DSB acts as a stronger barrier than a DMB and all ordering that is
+ * created by a DMB with specific options is also generated by a DSB with
+ * the same options.
  *)
 let dmb.full = DMB.ISH | DMB.OSH | DMB.SY | dsb.full
 let dmb.ld = DMB.ISHLD | DMB.OSHLD | DMB.LD | dsb.ld