refactor: remove osext dependency

What does this MR do?

Remove osext.

Why was this MR needed?

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 )

What's the best way to test this MR?

What are the relevant issue numbers?

Could potentially fix #1246 (closed)