remove crt feature flag (#21788)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/post_test.go

@@ -12,7 +12,6 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
-	"os"
 	"reflect"
 	"sort"
 	"strings"
@@ -2954,8 +2953,6 @@ func TestSetChannelUnread(t *testing.T) {
 }
 
 func TestSetPostUnreadWithoutCollapsedThreads(t *testing.T) {
-	os.Setenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS", "true")
-	defer os.Unsetenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS")
 	th := Setup(t).InitBasic()
 	defer th.TearDown()
 	th.App.UpdateConfig(func(cfg *model.Config) {