Remove generated file rules in make

This is all covered by update-codegen.sh now.

The old `make generated_files` rule still exists, but just prints a
warning.

hack/make-rules/update.sh

@@ -22,14 +22,6 @@ set -o pipefail
 KUBE_ROOT=$(dirname "${BASH_SOURCE[0]}")/../..
 source "${KUBE_ROOT}/hack/lib/init.sh"
 
-# If called directly, exit.
-if [[ "${CALLED_FROM_MAIN_MAKEFILE:-""}" == "" ]]; then
-    echo "ERROR: $0 should not be run directly." >&2
-    echo >&2
-    echo "Please run this command using \"make update\""
-    exit 1
-fi
-
 SILENT=${SILENT:-true}
 ALL=${FORCE_ALL:-false}
 

hack/make-rules/vet.sh

@@ -23,14 +23,6 @@ source "${KUBE_ROOT}/hack/lib/init.sh"
 
 cd "${KUBE_ROOT}"
 
-# If called directly, exit.
-if [[ "${CALLED_FROM_MAIN_MAKEFILE:-""}" == "" ]]; then
-    echo "ERROR: $0 should not be run directly." >&2
-    echo >&2
-    echo "Please run this command using \"make vet\""
-    exit 1
-fi
-
 # Filter out arguments that start with "-" and move them to goflags.
 targets=()
 for arg; do