Unused import

[luandy64]

https://github.com/singer-io/tap-google-sheets/blob/f1d1d43c6b74a8705e91e908c582e39c68464c0c/tap_google_sheets/schema.py#L3

I think this is safe to remove because it's only used in this one initialization, but it's not really used because that variable is overwritten moments later