Cleanup repository and remove outdated versions

[sephiroth-j]

The repo file contains 544 entries for drivers. Half of them are chromedriver. And many are outdated. I think it would be good to remove some of the old drivers: smaller file size, faster to parse, less memory footprint, reduced testing times and http calls during tests.

Here is my proposal.

For phantomjs, IE and Opera: remove all except the last release.
For Gecko: keep last three versions.
For Edge, Chrome and other Chromium based browser: keep only the last three versions.

And in general: only keep latest major-minor combination. E.g. remove "0.11.0" if "0.11.1" is present.

[treyturner]

Just a guest contributor here, but this could break builds that haven't been touched in a long time.