Remove references to some Montgomery curves
After all it looks like those won't become standard.
diff --git a/library/ecp.c b/library/ecp.c
index a802747..8703be0 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -98,10 +98,7 @@
#define ECP_SHORTWEIERSTRASS
#endif
-#if defined(MBEDTLS_ECP_DP_M221_ENABLED) || \
- defined(MBEDTLS_ECP_DP_M255_ENABLED) || \
- defined(MBEDTLS_ECP_DP_M383_ENABLED) || \
- defined(MBEDTLS_ECP_DP_M511_ENABLED)
+#if defined(MBEDTLS_ECP_DP_M255_ENABLED)
#define ECP_MONTGOMERY
#endif