Moto G 2014 without OS or any connection, stuck with fastboot and TWRP
I have had this exact problem with an XT1039. As you've deleted the system partition you'll need to restore to a factory ROM for the phone, which is on XDA.
Boot to recovery (power + volume down), and plug the phone in to your PC and you should have access to a minimal adb. Flash the factory image and it should then boot.

These instructions should help: https://forum.xda-developers.com/showthread.php?t=2542219