[DOCS] Removes abbrevtitles from parts

[lcawl]

Summary

This PR makes the changes necessary for the Kibana Guide to be built via asciidoctor (see elastic/docs#756).

It fixes the following build errors:

element partintro: validity error : Element partintro content does not follow the DTD... got (titleabbrev )

In particular, it removes abbreviated titles due to asciidoctor/asciidoctor#3132

@gchaps @schersh If you prefer to use the abbreviated title strings as the titles, that can be easily changed.

[skip ci]

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

- [ ] This was checked for cross-browser compatibility, including a check against IE11
- [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes [i18n support](https://github.com/elastic/kibana/blob/master/packages/kbn-i18n/README.md)

• Documentation was added for features that require explanation or tutorials
  - [ ] Unit or functional tests were updated or added to match the most common scenarios
  - [ ] This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-docs

[elasticmachine]

💔 Build Failed

• continuous-integration/kibana-ci/pull-request

[schersh]

Thanks for looking into this - LGTM