rxrpc: remove rxrpc_max_call_lifetime declaration

rxrpc_max_call_lifetime has been removed since
commit a158bdd3 ("rxrpc: Fix call timeouts"),
so remove it.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Link: https://lore.kernel.org/r/20220909064042.1149404-1-cuigaosheng1@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/rxrpc/ar-internal.h

@@ -782,7 +782,6 @@ void rxrpc_delete_call_timer(struct rxrpc_call *call);
  */
 extern const char *const rxrpc_call_states[];
 extern const char *const rxrpc_call_completions[];
-extern unsigned int rxrpc_max_call_lifetime;
 extern struct kmem_cache *rxrpc_call_jar;
 
 struct rxrpc_call *rxrpc_find_call_by_user_ID(struct rxrpc_sock *, unsigned long);