How Can I Remove Epiphany Without Removing Gnome?

Gnome-core is just a metapackage. You can remove it without much ill effect.

Its only provided files are a changelog and a copyright file. It won't "hold" dependencies installed, you run a minor risk there, but nothing major.

Reference

You need to remove the epiphany-browser package. And if you installed any extra packages:

sudo apt-get remove epiphany-browser epiphany-browser-data epiphany-browser-data epiphany-extensions