Remove imp import from xxxswf for python 3.12 compatability

[cccs-jh]

The imp module is removed in 3.12 and causes an error when loading xxxswf. The recommended replacement is importlib but here the use of imp is actually redundant. When yara isn't found the import yara statement already throws an ImportError for 3.5 and earlier, and for 3.6 and later it throws a ModuleNotFoundError which is a subclass of ImportError and is caught by the same try catch.