Remove doxygen tag

Remove a tag from a non-doxygen block
diff --git a/include/mbedtls/oid.h b/include/mbedtls/oid.h
index 239a37d..396bcdd 100644
--- a/include/mbedtls/oid.h
+++ b/include/mbedtls/oid.h
@@ -283,7 +283,7 @@
 
 /*
  * ECParameters namedCurve identifiers, from RFC 5480, RFC 5639, and SEC2
- * When adding new OID's, please update \c MBEDTLS_ECP_GRP_OID_MAX_SIZE
+ * When adding new OID's, please update MBEDTLS_ECP_GRP_OID_MAX_SIZE
  * in ecp.h
  */