oeqa: runtime: logrotate: Remove setup and tear down methods

oeqa: runtime: logrotate: Remove setup and tear down methods

Setup and tear down methods are executed even when the tests are disabled.
This lead to SSH being used to run commands on the target, and as it
might fail when no SSH server is present, we had to use
ignore_ssh_fails=True here.

Instead, run cleanup tasks in tests themselves and remove the tear down
method.

Also, the wtmp configuration file is not modified since the test was
modified a few years ago: there is no need to backup and restore it.

Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>