Remove obsolete IPaths attributes.

packages/application/src/frontend.ts

@@ -339,10 +339,6 @@ export namespace JupyterFrontEnd {
       readonly static: string;
       readonly settings: string;
       readonly themes: string;
-      readonly tree: string;
-      readonly docTree: string;
-      readonly workspaces: string;
-      readonly docWorkspaces: string;
       readonly hubPrefix?: string;
       readonly hubHost?: string;
       readonly hubUser?: string;

packages/application/src/lab.ts

@@ -280,10 +280,6 @@ export namespace JupyterLab {
       static: PageConfig.getOption('staticUrl'),
       settings: PageConfig.getOption('settingsUrl'),
       themes: PageConfig.getOption('themesUrl'),
-      tree: PageConfig.getOption('treeUrl'),
-      docTree: PageConfig.getOption('docTreeUrl'),
-      workspaces: PageConfig.getOption('workspacesUrl'),
-      docWorkspaces: PageConfig.getOption('docWorkspacesUrl'),
       hubHost: PageConfig.getOption('hubHost') || undefined,
       hubPrefix: PageConfig.getOption('hubPrefix') || undefined,
       hubUser: PageConfig.getOption('hubUser') || undefined,