Packaging: dh_install copies main and debug extension libs for main package.

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The dh_install which copies the Python extension for the main package also copies the dbg shared library.

https://github.com/DesignSparkRS/python3-geohash/blob/master/debian/rules#L25

Other variations of exclude pattern have either resulted in the same or neither library being copied.

This doesn't cause problems provided the -dbg package is not installed.