Workspaces: excise vendor from golang.sh

```
$ make
go version go1.20.4 linux/amd64
+++ [0506 13:21:33] Building go targets for linux/amd64
    ./cmd/kube-proxy (static)
    ./cmd/kube-apiserver (static)
    ./cmd/kube-controller-manager (static)
    ./cmd/kubelet (non-static)
    ./cmd/kubeadm (static)
    ./cmd/kube-scheduler (static)
    ./staging/src/k8s.io/component-base/logs/kube-log-runner (static)
    ./staging/src/k8s.io/kube-aggregator (static)
    ./staging/src/k8s.io/apiextensions-apiserver (static)
    ./cluster/gce/gci/mounter (non-static)
    ./cmd/kubectl (static)
    ./cmd/kubectl-convert (static)
    github.com/onsi/ginkgo/v2/ginkgo (non-static)
    ./test/e2e/e2e.test (test)
    ./test/conformance/image/go-runner (non-static)
    ./cmd/kubemark (static)
    github.com/onsi/ginkgo/v2/ginkgo (non-static)
    ./test/e2e_node/e2e_node.test (test)
```

before:
real	4m31.100s
user	21m1.466s
sys	2m23.546s

after:
real	3m46.591s
user	16m34.665s
sys	2m1.553s

hack/lib/golang.sh

@@ -76,9 +76,9 @@ kube::golang::server_targets() {
     cmd/kubelet
     cmd/kubeadm
     cmd/kube-scheduler
-    vendor/k8s.io/component-base/logs/kube-log-runner
-    vendor/k8s.io/kube-aggregator
-    vendor/k8s.io/apiextensions-apiserver
+    staging/src/k8s.io/component-base/logs/kube-log-runner
+    staging/src/k8s.io/kube-aggregator
+    staging/src/k8s.io/apiextensions-apiserver
     cluster/gce/gci/mounter
   )
   echo "${targets[@]}"
@@ -126,7 +126,7 @@ kube::golang::node_targets() {
     cmd/kube-proxy
     cmd/kubeadm
     cmd/kubelet
-    vendor/k8s.io/component-base/logs/kube-log-runner
+    staging/src/k8s.io/component-base/logs/kube-log-runner
   )
   echo "${targets[@]}"
 }
@@ -395,7 +395,8 @@ kube::golang::binaries_from_targets() {
     fi
 
     if [[ "${target}" =~ ^vendor/ ]]; then
-      # Strip vendor/ prefix, since we're building in gomodule mode.
+      # Strip vendor/ prefix, since we're building in gomodule mode.  This is
+      # for backwards compatibility.
       echo "${target#"vendor/"}"
       continue
     fi
@@ -795,7 +796,7 @@ kube::golang::build_some_binaries() {
 
         go test -c -o "$(kube::golang::outfile_for_binary "${package}" "${platform}")" \
           -covermode count \
-          -coverpkg k8s.io/...,k8s.io/kubernetes/vendor/k8s.io/... \
+          -coverpkg k8s.io/... \
           "${build_args[@]}" \
           -tags coverage \
           "${package}"