Remove GOOGLE_XPN_HOST_PROJECT env variable

[danawillow]

Even though this is only used in one test, we obnoxiously require it to be set when running any test. Since we have XPN support now, we can actually set up an XPN project in the test that uses this variable so we don't need it anymore. Or if we don't feel like doing that, we can at the very least only check it in the test where it gets used.

[danawillow]

#760 makes the variable no longer mandatory for all tests, keeping this open to track removing it altogether.

[rosbo]

Oupps, it was automatically closed when I merged #760

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 [email protected]. Thanks!