Updating dependencies and tidying modules

[kenshaw]

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This removes unused package dependenices declared in the go.{mod,sum} files, and updates all dependencies.

[kenshaw]

Hi, @rakyll really appreciate the work done on this driver!

I'm submitting this PR since there are some dependencies listed in go.{mod,sum} that are unnecessary. The usql project incorporates this driver. The extra declared dependency to gorm causes some issues with also incorporating the go-sqlite3 driver.

[skuruppu]

@kenshaw I don't think @rakyll works on this project anymore. We're continuing the work in https://github.com/cloudspannerecosystem/go-sql-spanner. Would you be able to make this PR against that repo? Then we can review and merge it in. Thanks a lot :)