Fix remaining non-determinism in fuzzer transcripts.

Both the C and Go code were sampling the real clock. With this, two
successive iterations of runner transcripts give the same output.

Change-Id: I4d9e219e863881bf518c5ac199dce938a49cdfaa
Reviewed-on: https://boringssl-review.googlesource.com/11222
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

FUZZING.md

diff --git a/FUZZING.md b/FUZZING.md
index 9f4edef..bf54829 100644
--- a/FUZZING.md
+++ b/FUZZING.md
@@ -60,4 +60,6 @@
 
 * Treat every cipher as the NULL cipher.
 
+* Use a hard-coded time instead of the actual time.
+
 This is to prevent the fuzzer from getting stuck at a cryptographic invariant in the protocol.