Removed final MBEDLTS_MD_C guard in PSA crypto library

There was one lingering MBEDTLS_MD_C that needed to be removed since
it is no longer needed.

Signed-off-by: John Durkop <john.durkop@fermatsoftware.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 78d0b9a..42d141c 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -453,9 +453,7 @@
     switch( type )
     {
         case PSA_KEY_TYPE_RAW_DATA:
-#if defined(MBEDTLS_MD_C)
         case PSA_KEY_TYPE_HMAC:
-#endif
         case PSA_KEY_TYPE_DERIVE:
             break;
 #if defined(MBEDTLS_AES_C)