Upgrade liblouis to 2.6.0.

This changes to the new mirror of the third_party library liblouis,
necessary because the project moved to github from an svn repository on
code.google.com.  Since the git mirroring infrastructure doesn't support
excluding parts of the tree, this means adding some GPL files and some files
without license headers.  The whitelist in tools/checklicenses/checklicenses.py
has been extended as needed.

One braille table (Hindi computer braille) is not available in liblouis
and has been removed.  A follow-up CL will add support for new braille
tables added in this release.

BUG=341951
R=dtseng@chromium.org, phajdan.jr@chromium.org

Review URL: https://codereview.chromium.org/579623003

Cr-Commit-Position: refs/heads/master@{#295679}

• DEPS[diff]
• chrome/browser/resources/chromeos/chromevox/host/chrome/braille_table_test.extjs[diff]
• third_party/liblouis/LICENSE[diff]
• third_party/liblouis/README.chromium[diff]
• third_party/liblouis/liblouis_nacl.gyp[diff]
• third_party/liblouis/overrides/liblouis/compileTranslationTable.c[Deleted - diff]
• third_party/liblouis/overrides/liblouis/config.h[diff]
• third_party/liblouis/overrides/liblouis/liblouis.h[diff]
• third_party/liblouis/overrides/tables/braille-patterns.cti[Deleted - diff]
• third_party/liblouis/overrides/tables/da.ctb[Deleted - diff]
• third_party/liblouis/tables.json[diff]
• tools/checklicenses/checklicenses.py[diff]