cmd/go: the .Deps field is used to determine whether test-variant packages have import cycles #52443
Description
Currently cmd/go uses the Deps field to determine cycles on test variant packages. This requires us to call collectDeps and examine the entire set of transitive dependencies for each test variant package even if we're not doing a go list command that requires presenting the transitive set of dependencies for each package in the output.
We should probably find another way to determine whether test-variant packages have import cycles.
cc @bcmills