Rename XXX_SINGLE_CIPHERSUITE -> XXX_CONF_SINGLE_CIPHERSUITE

This is in line with the other configurations options used
to hardcoded aspects of the SSL configuration.
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 2b7e9da..8290c51 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -3650,7 +3650,7 @@
  *
  * If this option is set, the API mbedtls_ssl_conf_ciphersuites() is removed.
  */
-//#define MBEDTLS_SSL_SINGLE_CIPHERSUITE MBEDTLS_SUITE_TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8
+//#define MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE MBEDTLS_SUITE_TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8
 
 /* \} SECTION: Compile-time SSL configuration */