Remove checks for copyright in charms

This patch removes the flake8 copyright plugin and configuration.

Change-Id: I65e362748e16efbc48055370f8f1590d4910c000
Signed-off-by: Dario Faccin <dario.faccin@canonical.com>
(cherry picked from commit 99325bd3a2891df4b88329931535619e96ae28ec)
16 files changed