use common js and defer it (#238)

This PR switches docs to use the custom common js code merged here: rapidsai/docs#286

Authors:
   - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:

docs/conf.py

@@ -132,5 +132,5 @@
 
 def setup(app):
     app.add_js_file("copybutton_pydocs.js")
-    app.add_css_file("params.css")
     app.add_css_file("https://docs.rapids.ai/assets/css/custom.css")
+    app.add_js_file("https://docs.rapids.ai/assets/js/custom.js", loading_method="defer")