[MM-57085] Remove UseNewSAMLLibrary experimental setting (#26392)

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

server/public/model/config.go

@@ -1009,7 +1009,6 @@ type ExperimentalSettings struct {
 	ClientSideCertCheck             *string `access:"experimental_features,cloud_restrictable"`
 	LinkMetadataTimeoutMilliseconds *int64  `access:"experimental_features,write_restrictable,cloud_restrictable"`
 	RestrictSystemAdmin             *bool   `access:"experimental_features,write_restrictable"`
-	UseNewSAMLLibrary               *bool   `access:"experimental_features,cloud_restrictable"`
 	EnableSharedChannels            *bool   `access:"experimental_features"`
 	EnableRemoteClusterService      *bool   `access:"experimental_features"`
 	DisableAppBar                   *bool   `access:"experimental_features"`
@@ -1034,10 +1033,6 @@ func (s *ExperimentalSettings) SetDefaults() {
 		s.RestrictSystemAdmin = NewBool(false)
 	}
 
-	if s.UseNewSAMLLibrary == nil {
-		s.UseNewSAMLLibrary = NewBool(false)
-	}
-
 	if s.EnableSharedChannels == nil {
 		s.EnableSharedChannels = NewBool(false)
 	}