Remove unneeded include

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/ecp.c b/library/ecp.c
index 6f53c1b..d9d5425 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -79,7 +79,6 @@
 
 #include "bn_mul.h"
 #include "ecp_invasive.h"
-#include "bignum_core.h"
 
 #include <string.h>