Move license out of Doxygen comment

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/bignum_core.h b/library/bignum_core.h
index 8e227f8..dc802ab 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -6,6 +6,9 @@
  *  modules should use the high-level modular bignum interface (bignum_mod.h)
  *  or the legacy bignum interface (bignum.h).
  *
+ */
+
+/*
  *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0
  *