Remove fillins/openssl_util

The only user of the tiny utility class to clear the error stack
was verify_certificate_chain, which can have it in it's anonymous
namespace.

It was however, used to great effect as a horrible dirty cheat to get
us openssl/base.h during the conversion. That time is past, so just
let us include <openssl/base.h> normally, and get rid of this.

Bug: 668
Change-Id: Ie8537d5b1d6789acb35182f3d781f7505ad79109
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/64188
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Auto-Submit: Bob Beck <bbe@google.com>
diff --git a/pki/path_builder.h b/pki/path_builder.h
index 48f0666..9aae757 100644
--- a/pki/path_builder.h
+++ b/pki/path_builder.h
@@ -7,8 +7,8 @@
 
 #include <memory>
 #include <vector>
-#include "fillins/openssl_util.h"
 
+#include <openssl/base.h>
 
 #include "cert_errors.h"
 #include "input.h"