Remove unnecessary wrapper flags

Drop KUBE_GOFLAGS, KUBE_GOGCFLAGS, KUBE_GOLDFLAGS references
from the build infrastructure. There are some usages still
for KUBE_GOFLAGS, so we should print a deprecation message
until all those are fixed. If both KUBE_GOFLAGS and GOFLAGS
are just then we just bail out.

hack/lib/golang.sh

@@ -624,9 +624,9 @@ kube::golang::build_binaries() {
 
     # Use eval to preserve embedded quoted strings.
     local goflags goldflags gogcflags
-    eval "goflags=(${KUBE_GOFLAGS:-})"
-    goldflags="${KUBE_GOLDFLAGS:-} $(kube::version::ldflags)"
-    gogcflags="${KUBE_GOGCFLAGS:-}"
+    eval "goflags=(${GOFLAGS:-})"
+    goldflags="${GOLDFLAGS:-} $(kube::version::ldflags)"
+    gogcflags="${GOGCFLAGS:-}"
 
     local use_go_build
     local -a targets=()