[MM-53086] Remove SendWelcomePost A/B test and feature (#23733)

Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/feature_flags.go

@@ -48,9 +48,6 @@ type FeatureFlags struct {
 
 	CommandPalette bool
 
-	// A/B Test on posting a welcome message
-	SendWelcomePost bool
-
 	PostPriority bool
 
 	// Enable WYSIWYG text editor
@@ -90,7 +87,6 @@ func (f *FeatureFlags) SetDefaults() {
 	f.InsightsEnabled = false
 	f.CommandPalette = false
 	f.CallsEnabled = true
-	f.SendWelcomePost = true
 	f.PostPriority = true
 	f.PeopleProduct = false
 	f.ReduceOnBoardingTaskList = false

server/public/model/post.go

@@ -45,7 +45,6 @@ const (
 	PostTypeChannelRestored        = "system_channel_restored"
 	PostTypeEphemeral              = "system_ephemeral"
 	PostTypeChangeChannelPrivacy   = "system_change_chan_privacy"
-	PostTypeWelcomePost            = "system_welcome_post"
 	PostTypeAddBotTeamsChannels    = "add_bot_teams_channels"
 	PostTypeSystemWarnMetricStatus = "warn_metric_status"
 	PostTypeMe                     = "me"
@@ -434,7 +433,6 @@ func (o *Post) IsValid(maxPostSize int) *AppError {
 		PostTypeChangeChannelPrivacy,
 		PostTypeAddBotTeamsChannels,
 		PostTypeSystemWarnMetricStatus,
-		PostTypeWelcomePost,
 		PostTypeReminder,
 		PostTypeMe:
 	default:

server/public/model/post_test.go

@@ -925,7 +925,7 @@ func TestPostForPlugin(t *testing.T) {
 
 	t.Run("non post type custom_up_notification for plugin should have requested features prop", func(t *testing.T) {
 		p := &Post{
-			Type: PostTypeWelcomePost,
+			Type: PostTypeReminder,
 		}
 		props := make(StringInterface)
 		props["requested_features"] = "test_requested_features_map"