Revert 2 commits to `git-changelog`

- Revert "FIX: check if un-pushed commits". This reverts commit bd80a4e51255d5d64ebfbb6ad6c28f44ef867470.

- Revert "Add check for no changes in the tree (no sub-modules)". This reverts commit f2a41c54b1a2d64cf09c537308976392e8a403b7.

Resolves #234