Replace with standard libraries such as pathlib

[armijnhemel]

A lot of the code in certain files, such as src/commoncode/paths.py and src/commoncode/filetype.py and possible others can be replaced by standard methods from the pathlib module. This has a few benefits:

1. less maintenance on your part
2. pathlib has seen more testing than your code
3. possible optimisations in pathlib

[armijnhemel]

I understand why this code was written, because pathlib was added in Python 3.4, around the same time that Scancode was started, so it was probably necessary back then. But it has been years, so probably it is good time to see if the code can be retired.