Remove reliable websockets configuration (#19040)

The feature is stable enough to be removed
as a config knob.

For backwards compatiblity with older mobile
clients, we keep sending the config param
as true for client config requests.

https://community-daily.mattermost.com/boards/workspace/zyoahc9uapdn3xdptac6jb69ic/285b80a3-257d-41f6-8cf4-ed80ca9d92e5/495cdb4d-c13a-4992-8eb9-80cfee2819a4/7m95frqbk9o8zxin6xo9c7iusoh

```release-note
NONE
```

config/client.go

@@ -94,7 +94,8 @@ func GenerateClientConfig(c *model.Config, telemetryID string, license *model.Li
 
 	props["CloudUserLimit"] = strconv.FormatInt(*c.ExperimentalSettings.CloudUserLimit, 10)
 
-	props["EnableReliableWebSockets"] = strconv.FormatBool(*c.ServiceSettings.EnableReliableWebSockets)
+	// TODO: remove this when the mobile client release reaches 1.52.
+	props["EnableReliableWebSockets"] = strconv.FormatBool(true)
 
 	// Set default values for all options that require a license.
 	props["ExperimentalEnableAuthenticationTransfer"] = "true"