Delete files and folders after parallel_stereo execution

[ShashankBice]

Is your feature request related to a problem? Please describe.
parallel_stereo clean up takes some time, which can be improved if files and folders are deleted in parallel.

Describe the solution you'd like
I propose to replace this for loop with parallel invocations to clear these up using all available threads at disposal.

Describe alternatives you've considered
Before this option in parallel_stereo existed, I used to do this myself in a custom python script using parallel techniques.

Additional context
I will be very happy to provide a Pull request by next week if it is of value.

[oleg-alexandrov]

Sure. Looking forward to a pull request.