Documentation: Remove the "rhash_entries=" from kernel-parameters.txt

"rhash_entries" belonged to the routing cache that has been removed in
commit 89aef892 ("ipv4: Delete routing cache.").
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240614092134.563082-1-thuth@redhat.com

Documentation/admin-guide/kernel-parameters.txt

@@ -5763,9 +5763,6 @@
 		2	The "airplane mode" button toggles between everything
 			blocked and everything unblocked.
 
-	rhash_entries=	[KNL,NET]
-			Set number of hash buckets for route cache
-
 	ring3mwait=disable
 			[KNL] Disable ring 3 MONITOR/MWAIT feature on supported
 			CPUs.