`dolt merge` does not print all merge stats if using `remotes/` syntax

All merges that complete without error should print a result line `Updating ...`. Currently, the `toHash` is calculated using the `hashof()` function which does not accept the `remotes/` prefix. Thus, if merging with using this syntax, you will get an error that says the hash was unable to be calculated. Merge stats calculation needs to be updated to print correctly when using the `remotes/` prefix.