test: remove unused variable
test: remove unused variable

This fixes linting.

https://github.com/nodejs/node-gyp/pull/1561
Reviewed-By: Refael Ackermann <0604a90ccdde7a0adfa2ff3857349859a7209740@gmail.com>

nodejs/node-gyp,nodegit/node-gyp,nodegit/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodejs/node-gyp,nodegit/node-gyp