Not only was watchtower mode never implemented, but the bits that
we had were removed some time ago. It doesn't seem likely we'll
move forward with a "watchtower-mode" ChannelMonitor, instead
we'll likely have some other, separate struct for this.
Previously, in each of our fuzz tests we had a dummy test which
had a hard-coded hex string which it passed into the fuzz target
so that when a failing test case was found, its hex could be
copied into the test and you could run cargo test to analyze the
failure. However, this was somewhat unwieldy as converting large
tests back and forth between hex and raw files is quite annoying.
Instead, we replace each of those tests with a test in each target
that looks for files in fuzz/test_cases and runs each file it finds.
Since we're editing every bin target anyway, we also automate adding
no_main to libfuzzer builds with #![cfg_attr].
