ssl_ticket.h: Fix note in API documentation

Since the merge of #8574 it is not the case
anymore that the lifetime of keys is twice
the lifetime of tickets.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/include/mbedtls/ssl_ticket.h b/include/mbedtls/ssl_ticket.h
index 5842049..a1e70d4 100644
--- a/include/mbedtls/ssl_ticket.h
+++ b/include/mbedtls/ssl_ticket.h
@@ -108,8 +108,7 @@
  *                  least as strong as the strongest ciphersuite
  *                  supported. Usually that means a 256-bit key.
  *
- * \note            The lifetime of the keys is twice the lifetime of tickets.
- *                  It is recommended to pick a reasonable lifetime so as not
+ * \note            It is recommended to pick a reasonable lifetime so as not
  *                  to negate the benefits of forward secrecy.
  *
  * \return          0 if successful,
@@ -145,8 +144,7 @@
  * \note            \c klength must be sufficient for use by cipher specified
  *                  to \c mbedtls_ssl_ticket_setup
  *
- * \note            The lifetime of the keys is twice the lifetime of tickets.
- *                  It is recommended to pick a reasonable lifetime so as not
+ * \note            It is recommended to pick a reasonable lifetime so as not
  *                  to negate the benefits of forward secrecy.
  *
  * \return          0 if successful,