Fix TestAccComputeRegionBackendService_ilbUpdateBasic, TestAccComputeBackendService_trafficDirectorUpdateBasic

[emilymye]

Backend services have weird API behavior around consistentHash (b/155442129) - we need to add in a custom encoder/decoder to remove the field when reading/sending to API

[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 👉 hashibot-feedback@hashicorp.com. Thanks!