Remove version specific download links

[markwalkom]

Here.

Otherwise we lock ourselves into having to update the links constantly. Instead we should use things like https://download.elastic.co/elasticsearch/elasticsearch/elasticsearch-latest.zip :)

[monicasarbu]

It's great to be able to download the latest package for Elasticsearch, but I think in the getting started guide it's better to choose what version of Elasticsearch and Kibana work better with each Beat release. It might be that an older version of a Beat doesn't work with the latest Elasticsearch or Kibana.

[dedemorton]

Giving users the exact commands to run makes it much easier for them to get started. I vote for keeping the version-specific commands and updating the doc when required. It's a quick change from a doc perspective, but it makes the user experience much better.

[dedemorton]

For now, we will leave the version-specific information to ensure that Beats users get the version of Elasticsearch and Kibana that works best with Beats.