The only thing that works for me, is the line commented out in the screenshot below:
Comment the InsertLinkViaTreeDialog
I Tried lots of solutions provided in the community but didn't work for me except the one below:
https://community.sitecore.net/developers/f/8/t/863
http://www.bugdebugzone.com/2015/06/sitecore-8-general-link-field-target_23.html
Any Clue? Which direction should we move with?