Clean up unused GetUploadEnv() in cache code

Stan Hurequested to merge
sh-cleanup-cache-upload-env into main

What does this MR do?

GetUploadEnv() was originally used to pass environment variables to the cache uploader for GetUploadURL(), but they have moved into the GoCloudURL structure, so this method is no longer needed. Remove all references to this method.

Why was this MR needed?

To eliminate dead code.

What's the best way to test this MR?

What are the relevant issue numbers?

Edited by Stan Hu

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