refactor(controller): stop auto-setting RUNNER_FEATURE_FLAG_EPHEMERAL (#1385)

This feature flag was provided from ARC to runner container automatically to let it use `--ephemeral` instead of `--once` by default. As the support for `--once` is being dropped from the runner image via #1384, we no longer need that.

Ref #1196

test/e2e/e2e_test.go

@@ -198,7 +198,6 @@ type env struct {
 	githubTokenWebhook                                       string
 	testEnterprise                                           string
 	testEphemeral                                            string
-	featureFlagEphemeral                                     *bool
 	scaleDownDelaySecondsAfterScaleOut                       int64
 	minReplicas                                              int64
 	dockerdWithinRunnerContainer                             bool
@@ -234,10 +233,6 @@ func initTestEnv(t *testing.T) *env {
 	e.testEphemeral = testing.Getenv(t, "TEST_EPHEMERAL", "")
 	e.testJobs = createTestJobs(id, testResultCMNamePrefix, 20)
 
-	if ephemeral, err := strconv.ParseBool(testing.Getenv(t, "TEST_FEATURE_FLAG_EPHEMERAL", "")); err == nil {
-		e.featureFlagEphemeral = &ephemeral
-	}
-
 	e.scaleDownDelaySecondsAfterScaleOut, _ = strconv.ParseInt(testing.Getenv(t, "TEST_RUNNER_SCALE_DOWN_DELAY_SECONDS_AFTER_SCALE_OUT", "10"), 10, 32)
 	e.minReplicas, _ = strconv.ParseInt(testing.Getenv(t, "TEST_RUNNER_MIN_REPLICAS", "1"), 10, 32)
 
@@ -308,10 +303,6 @@ func (e *env) installActionsRunnerController(t *testing.T) {
 		fmt.Sprintf("ENTERPRISE_RUNNER_MIN_REPLICAS=%d", e.minReplicas),
 	}
 
-	if e.featureFlagEphemeral != nil {
-		varEnv = append(varEnv, fmt.Sprintf("RUNNER_FEATURE_FLAG_EPHEMERAL=%v", *e.featureFlagEphemeral))
-	}
-
 	if e.useApp {
 		varEnv = append(varEnv,
 			"ACCEPTANCE_TEST_SECRET_TYPE=app",