r/html_reports: Move $statistics_file to harness cache

The file only stores data from the last run.  Its absence just causes
the "since last run"-numbers to be wrong for a single run.  Based on
that it seems like it fits more in the new state dir rather than the
"logs" dir.

Signed-off-by: Niels Thykier <niels@thykier.net>
r/config: Remove $statistics_file from the sample config

Signed-off-by: Niels Thykier <niels@thykier.net>
L::L::Manifest: Retry using C::Accessor getters

Some time ago, the getters generated for Lintian::Lab::Manifest would
just randomly return undef for no apparent reason.  Manually written
getters would work just fine in the same case.

The generated getters have been reinstated on the basis that they seem
to work fine now.

Signed-off-by: Niels Thykier <niels@thykier.net>