pydepends: recognize extension modules with limited ABI (*.abi3.so)

For example, python-autobahn has the following file,

/usr/lib/python3.10/site-packages/_nvx_utf8validator.abi3.so

And namcap didn't find it when handling 'import _nvx_utf8validator'

python-autobahn W: Referenced library '_nvx_utf8validator' is an uninstalled dependency

PS. Also removes an unused variable.