Remove osext

What does this MR do?

Remove osext.

As of go 1.8+ Executable is part of the std lib and osext is deprecated ( see https://github.com/kardianos/osext/issues/20 and https://github.com/kubernetes/kubernetes/issues/80127 )

TODO

• Added the Changelog (e.g. Changelog: feature) trailer to the commits that need to be included in the changelog
• Added unit tests (if required)
• Added acceptance tests (if required)
• Documentation (if required)
• Code review guidelines
• Go Style guidelines