1. I guess you use the stock dialer. If so, when on the contacts tab, go to settings and select customize. There you can choose the sources to display, and you can leave gmail only.
2. Removing accounts can be achieved by going to phones settings, then accounts and then removing the required account, google here. However, as the google account is so fundamental in Android, removing it is usually not easy (as many things rely on it). Maybe the only way is to go back to manufacturer's settings.
Sent from my LG-P714 using xda app-developers app
Phone: LG L7 II P714
ROM: LG Stock 4.1.2
Recovery: CWM v184.108.40.206
Tweaks: Xposed (GravityBox, Greenify, App Settings, ClockColorChanger, All Notifications Expanded), Nova Launcher Prime