Revert "Replace '_' with space in field name."

This reverts commit 22ec5ab3828e1c6a8d356f3a7b244970ab723cd2.
Converting underscores to spaces ONLY on labels

See comments on https://github.com/Anahkiasen/former/commit/22ec5ab3828e1c6a8d356f3a7b244970ab723cd2#commitcomment-4543228 for some history