Drop .arclint file

Summary:
Lately, submitting patches has become very annoying because of cppcheck's
false positive error messages. After doing some research, no reasonable
solution have been found to this annoying problem so let's get rid of the
.arclint file. If we've missed something during the code review, our CI
will spot it. Although CI doesn't check spelling, we have other ways to
detect typos, e.g. EBN.

Reviewers: #kwin, apol

Reviewed By: apol

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28119