Hi,

Whilst working on the Reproducible Builds effort [0], we noticed that
docker-credential-gcr could not be built reproducibly.

This is because the testsuite does not completely clean up after itself,
meaning that if the tests are skipped the contents of the binary files
differ and is thereby unreproducible.

Patch attached that deletes the two .json files.

 [0] https://reproducible-builds.org/


Regards,