For regular webstatscollector installs, use latest version

Since oxygen was running an outdated version of webstatscollector,
pageviews were miscounted for some weeks (bug 70295). To avoid such
regressions from happening again, we ensure that the latest version of
webstatscollector gets used.

Thereby, we run into risks of silent updates. But since
webstatscollector is built and developed in-house, we prefer this risk
to having an outdated package ruin data again.

We do not ensure the latest webstatscollector version for kafkatee's
webstatscollector, as that is a custom build from the kafka branch.

Bug: 70295
Change-Id: If012740343194603d1f03b6daf9b54cfb728d2ff