Given that a MerkleAuditProof only proves an inclusion path for a tree of a specific size, a tree_size parameter was added to it in  https://crrev.com/89f010d82559c73e7d23cbf067137ceb1df698df to keep track of which tree the proof was for. Because of this, it's no longer necessary to store the tree size separately in LogDnsClient::AuditProofQuery. Instead, it can just use the tree_size member of the MerkleAuditProof.

The QueryAuditProof method still takes the tree_size as a separate parameter, so as to not make the proof parameter a mixed in/out parameter, which could be confusing.

BUG=624894

Review-Url: https://codereview.chromium.org/2485653002
Cr-Commit-Position: refs/heads/master@{#430604}