[SDK-302] Remove backoff library

[vbrodsky]

Story: https://labelbox.atlassian.net/browse/SDK-302

The backoff library we use is old and it conflicts with the version the lightning-ai library used by Ancestry

Upon further inspection, I have discovered this library can be replaced with google.api_core.retry we use elsewhere in our code

This will execute exponential backoff for 2 minutes (default), like

tests/integration/annotation_import/test_bulk_import_request.py::test_wait_till_done 
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