Remove Permalink Preview Feature Flag (#23731)

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

server/public/model/feature_flags.go

@@ -73,7 +73,6 @@ func (f *FeatureFlags) SetDefaults() {
 	f.AppsEnabled = true
 	f.PluginApps = ""
 	f.PluginFocalboard = ""
-	f.PermalinkPreviews = true
 	f.BoardsFeatureFlags = ""
 	f.BoardsDataRetention = false
 	f.NormalizeLdapDNs = false