Corrects documentation issues

Commit corrects incorrect docs in
ecdh.h and config.h.

Signed-off-by: Thomas Daubney <thomas.daubney@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index c6882db..7916587 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -779,8 +779,7 @@
  *
  * \note  This option only works with the default software implementation of
  *        elliptic curve functionality. It is incompatible with
- *        MBEDTLS_ECP_ALT, MBEDTLS_ECDH_XXX_ALT, MBEDTLS_ECDSA_XXX_ALT
- *        and MBEDTLS_ECDH_LEGACY_CONTEXT.
+ *        MBEDTLS_ECP_ALT, MBEDTLS_ECDH_XXX_ALT, MBEDTLS_ECDSA_XXX_ALT.
  */
 //#define MBEDTLS_ECP_RESTARTABLE