Fix cmdline args to generate-notice-files.py

-e should be provided multiple times to pass a list. This fixes
stripping of the NOTICE file on /system to not have /product,
/vendor and /product_services entries in it.

Previously it was trying to stirp entries from the
vendor,product,product_services subdir.

Bug: 118089975
Test: m sync, inspect NOTICES file
Change-Id: I7c336b1c593565a98aa4976305f8b69bbd0c09b5