I used Jlinked for login to my website with Jomsocial, but after clicking LinkedIn, the registration page come back with some "unnecessary" user profile fields like "Favourite Book" and a few other fields which I don't know why the fields came from. These fields should've been there. Looking at the URL they seems to be generated by jlinked. Can you tell me which possible part of Jlinked could have generated these unnecessary "User profile" section? See the screenshot. The URL name bears the jlinked part.
You likely have the "User - Profile" plugin enabled in Joomla. That's a built-in profile system for Joomla, which is pretty limited. It's automatically added to our registration form if it's enabled. If you don't want it, disable it.
The other possibility is that those fields are from JomSocial or another extension you're integrating JLinked with, but I don't think that's the case.