Limit to 79 characters per line in the three files with most violations

This makes a step towards #1986 (closed) by fixing the line length in the following files:

• pmb.aportgen.device.py
• pmb.helpers.aportupgrade.py
• pmb.parse.arguments.py

As of writing these are the 3 files with the highest number of line-length violations in the repo.

EDIT by ollieparanoid: removed "closing" verb so gitlab doesn't close the issue 😉