Make hack scripts use go install and assume PATH

Now that they all call setup_env, we don't need find-binary (I think).
That was originally meant to hide the diff between docker and local
builds but all these tools do local builds anyway.

hack/verify-fieldname-docs.sh

@@ -28,12 +28,7 @@ source "${KUBE_ROOT}/hack/lib/util.sh"
 
 kube::golang::setup_env
 
-make -C "${KUBE_ROOT}" WHAT=cmd/fieldnamedocscheck
-
-# Find binary
-fieldnamedocscheck=$(kube::util::find-binary "fieldnamedocscheck")
-
-result=0
+GOPROXY=off go install ./cmd/fieldnamedocscheck
 
 find_files() {
   find . -not \( \
@@ -55,10 +50,11 @@ find_files() {
 
 versioned_api_files=$(find_files) || true
 
+result=0
 for file in ${versioned_api_files}; do
   package="${file%"/types.go"}"
   echo "Checking ${package}"
-  ${fieldnamedocscheck} -s "${file}" || result=$?
+  fieldnamedocscheck -s "${file}" || result=$?
 done
 
 exit ${result}