lddtree.py: relicense to BSD-3 to silence Debian licensecheck.pl.
lddtree.py: relicense to BSD-3 to silence Debian licensecheck.pl.

Cherry-picking from upstream -

http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-projects/\
pax-utils/lddtree.py?r1=1.20&r2=1.21

BUG=None
TEST=Ran licensecheck.pl

Change-Id: I736f53fd61aea955f9f91c2267297d352390e4c0
Reviewed-on: https://gerrit.chromium.org/gerrit/46311
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Commit-Queue: Ryan Cui <5ce1592d53754a87a44fc2eb7b63d5f77cf50fdb@chromium.org>
Tested-by: Ryan Cui <5ce1592d53754a87a44fc2eb7b63d5f77cf50fdb@chromium.org>

bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite