Remove obsolete theme.css and its reference

Author: jelveh

src/gui/puter-gui.json

@@ -19,7 +19,6 @@
             "/css/normalize.css",
             "/lib/jquery-ui-1.13.2/jquery-ui.min.css",
             "/css/style.css",
-            "/css/theme.css",
             "/css/dashboard.css"
         ],
         "js_paths": [