MM-34125: Remove WebSocketDelay feature flag (#17441)

It has been soaked for enough time in community-daily
and also in community. Enabling it for all.

```release-note
TCP_NO_DELAY is disabled for websocket connections
to allow for higher throughput
```

https://mattermost.atlassian.net/browse/MM-34125

model/feature_flags.go

@@ -34,8 +34,6 @@ type FeatureFlags struct {
 
 	// Toggle on and off support for Files search
 	FilesSearch bool
-	// Feature flag to control setting the TCP_NO_DELAY setting for websockets.
-	WebSocketDelay bool
 
 	// Control support for custom data retention policies
 	CustomDataRetentionEnabled bool
@@ -52,7 +50,6 @@ func (f *FeatureFlags) SetDefaults() {
 
 	f.PluginIncidentManagement = "1.7.0"
 	f.PluginApps = ""
-	f.WebSocketDelay = false
 	f.CustomDataRetentionEnabled = false
 }