Remove mentions of RSA-PSK key exchange from documentation

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index 2c8f91b..6fa2e6a 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -3058,7 +3058,7 @@
  *          library/ssl*_server.c
  *
  * This module is used by the following key exchanges:
- *      RSA, DHE-RSA, ECDHE-RSA, RSA-PSK
+ *      RSA, DHE-RSA, ECDHE-RSA
  *
  * Requires: MBEDTLS_BIGNUM_C, MBEDTLS_OID_C
  */