go back to using the upstream gcp-detector

[trentm]

https://github.com/open-telemetry/opentelemetry-js-contrib/pull/3007/files added a more capable gcp-detector upstream. Our current local detector-gcp.js is likely a downgrade now. Note that the upstream detector may (likely?) still have the issue with spans being created for its requests, so there is a judgment call to make if that is the case.

[david-luna]

next release open-telemetry/opentelemetry-js#6008 is going to provide a fix by setting the context manager just at the start of the SDK. I think this can be planned for next iteration