Better duplication clean

Until now, removing duplicated libraries was done "blindly", based only in the name. This has the inconvenient that if a library already available in the extension snap is recompiled in the snap, the maintainer must be careful to ensure that it is kept in the final snap.

This MR replaces the old bash script with a python one that compares the files, and only removes them if the contents are the same. This ensures that, if the library inside the snap is different, that one will be included.

Currently this code only removes files with ".so." in their name. An improvement could be to also check for icons or other file types.