Revert "add non-free files to quinn-diff (and to wanna-build)"

Revert "add non-free files to quinn-diff (and to wanna-build)"

This reverts commit 636fd44b6b3b8f343eb53c4ef2dd053fb91bd4d6.

This commit breaks merging and performance.

Traceback (most recent call last):
  File "/org/wanna-build/triggers/filter-nonfree", line 49, in <module>
    main()
  File "/org/wanna-build/triggers/filter-nonfree", line 44, in main
    okpkgs = check_source(oklist, open(sys.argv[3]), outfile(name, sys.argv[3]))
  File "/org/wanna-build/triggers/filter-nonfree", line 13, in check_source
    if pkg.Section['Section'].startswith('non-free'):
KeyError: 'Section'

Signed-off-by: Philipp Kern <pkern@debian.org>