[Patch] improve usage description and remove unused library in mergeinfo-sanitizer.py

Hi,

The "re" package is never used in the mergeinfo-sanitizer.py script,
hence it can be removed.
Also improved the "usage" description to show the usage of the options.
I am working on this script to enhance/optimize it further.

I have attached a patch and the log message with this mail.

Thanks and regards
Prabhu