Remove mention of squash commits (GH-165)
Remove mention of squash commits (GH-165)

Commits will be squashed right before the PR gets merged
via GitHub UI.
It is preferred that commits in a PR are not squashed so tha
we can view the diff from one commit to another.

Closes https://github.com/python/devguide/issues/164
jython/devguide,jython/devguide,ezio-melotti/devguide,jython/devguide,jeff5/jython-devguide,jeff5/jython-devguide,jeff5/jython-devguide