Use only `MBEDTLS_ECP_WITH_MPI_UINT` to switch between the ecp variants

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/ecp_invasive.h b/library/ecp_invasive.h
index 456ac21..c4a0a4d 100644
--- a/library/ecp_invasive.h
+++ b/library/ecp_invasive.h
@@ -40,23 +40,13 @@
     MBEDTLS_ECP_MOD_SCALAR
 } mbedtls_ecp_modulus_type;
 
-/* Requred macros for ECP split.
- * If MBEDTLS_ECP_WITH_MPI_UINT is defined the new bignum interface is used.
- */
-#if !defined(MBEDTLS_ECP_WITH_MPI_UINT)
-
 /* Provide a commented-out definition so that `check_names.py` knows that
  * it's not a typo.
  * MBEDTLS_ECP_WITH_MPI_UINT must not be defined within config files, but
- * only on the command line, as otherwise both ECP implementations will be
- * built.
+ * only on the command line.
  */
 //#define MBEDTLS_ECP_WITH_MPI_UINT
 
-/* Enable the old bignum interface. */
-#define MBEDTLS_ECP_WITH_MPI_STRUCT
-#endif
-
 typedef enum {
     MBEDTLS_ECP_VARIANT_NONE            = 0,
     MBEDTLS_ECP_VARIANT_WITH_MPI_STRUCT = 1,