Delete crashed if a fullNode contained a valueNode directly. This bug is
very unlikely to occur with SecureTrie, but can happen with regular
tries. This commit also introduces a randomised test which triggers all
trie operations, which should prevent such bugs in the future.
Credit for finding this bug goes to Github user @rjl493456442.
(cherry picked from commit c3a77d626831b4ffe37ed4f8640e67e70ad5b220)