Fix documentation of SQlite3Adapter.columns

As of https://github.com/rails/rails/commit/e781aa31fc52a7c696115302ef4d4e02bfd1533b SQLite3Column has been dropped.
Remove references to SQLite3Column from documentation
Merge pull request #16290 from a3gis/master

[ci skip] Fix documentation of SQLite3Adapter.columns where SQLite3Column was removed in e781aa31fc52a7c696115302ef4d4e02bfd1533b