As posted in a reply above, if you go to the XDA link here: http://forum.xda-developers.com/g4/general/guide-lg-g4-stock-firmware-to-stock-kdz-t3107848 and follow the instructions to download and flash stock firmware image, you will be back up and running with a new out of the box condition.
There is also a Puerto Rico version you can flash that has no AT&T bloatware on it but does not support VOLTE. Thinking really hard about doing that as the bloatware is rather ridiculous.
Good luck!