improve(wrangler): fix subdomain tests (#7210)

Many tests had mocks that weren't called,
or had false assertions about not updating subdomain routes when they
actually were being updated.

Additionally, available_on_subdomain is now unecessary during
script-upload, as it is not read there, due to being handled entirely
within triggers-deploy. This also saves a double call to get /subdomain
in the new-api path.

The get/update subdomain helpers are refactored from deploy/version
tests, and unified to standardize default workername and legacyEnv.

I wanted to remove the getSubdomain mock from mockUpload entirely, but
there were a bit too many callsites... At least every test now that
makes assertions about workers.dev deployments does explicitly reset the
mock return value.

Author: taylorlee

.changeset/clean-tigers-breathe.md

@@ -0,0 +1,5 @@
+---
+"wrangler": patch
+---
+
+Avoid an unnecessary GET request during `wrangler deploy`.