The rationale here is the same as the last commit: since this crate
exclusively parses SQL, there's no need to restate that in every type
name. (The prefix seems to be an artifact of this crate's history as a
submodule of Datafusion, where it was useful to explicitly call out
which types were related to SQL parsing.)
This commit has the additional benefit of making all type names
consistent; over type we'd added some types which were not prefixed with
"SQL".
