How to disconnect Gmail link from Yahoo

I assume you have your yahoo account set to forward to gmail so remove the forwarding setting.  If it's similar to the att/yahoo webmail, click the gear->settings->accounts and choose the account.  The resulting pane includes a field for forwarding.  Clear it and save the updated settings.

Update:

I answered here before I saw your post in that other thread.  Obviously you should now see the techniques are similar, just a different field in the same account settings pane (still assuming you are forwarding).