Remove "SQL" prefix from types

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".

src/lib.rs

@@ -18,10 +18,10 @@
 //! Syntax Tree (AST).
 //!
 //! ```
-//! use sqlparser::dialect::GenericSqlDialect;
+//! use sqlparser::dialect::GenericDialect;
 //! use sqlparser::parser::Parser;
 //!
-//! let dialect = GenericSqlDialect {}; // or AnsiSqlDialect
+//! let dialect = GenericDialect {}; // or AnsiSqlDialect
 //!
 //! let sql = "SELECT a, b, 123, myfunc(b) \
 //!            FROM table_1 \