Remove `MBEDTLS_KEY_EXCHANGE_RSA_ENABLED` config option

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/tests/include/test/ssl_helpers.h b/tests/include/test/ssl_helpers.h
index ef4927f..3ba314f 100644
--- a/tests/include/test/ssl_helpers.h
+++ b/tests/include/test/ssl_helpers.h
@@ -66,8 +66,7 @@
 
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
 
-#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||  \
-    defined(MBEDTLS_KEY_EXCHANGE_RSA_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED)
 #define MBEDTLS_CAN_HANDLE_RSA_TEST_KEY
 #endif