Build and test PK without MD

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 5fe9849..7582daa 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -359,7 +359,7 @@
 #endif
 
 #if defined(MBEDTLS_PK_C) && \
-    ( !defined(MBEDTLS_MD_C) || ( !defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_ECP_C) ) )
+    !defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_ECP_C)
 #error "MBEDTLS_PK_C defined, but not all prerequisites"
 #endif