chore: remove unused kokoro config files (#191)

* changes without context

        autosynth cannot find the source of changes triggered by earlier changes in this
        repository, or by version upgrades to tools such as linters.

* cleanup: removes unused kokoro config files

* cleanup: removes unused kokoro config files

Removes unused kokoro files from the java library template. We have
stopped running some of these due to Github quota issues.

* fix:reverts back samples.cfg files

The files presubmit/samples.cfg and nightly/samples.cfg should remain in
the java template repository.

Co-authored-by: Jeffrey Rennie <[email protected]>

Source-Author: Thiago Nunes <[email protected]>
Source-Date: Thu Aug 6 09:48:58 2020 +1000
Source-Repo: googleapis/synthtool
Source-Sha: 4530cc6ff080ef8aca258c1ec92c4db10a1bbfb4
Source-Link: googleapis/synthtool@4530cc6

Author: yoshi-automation