Remove build references to third_party/cygwin

There's test running dependencies in blink and buildbot,
so the directory/DEPS can't be removed right now. For the
time being, remove the build related entries.

R=maruel@chromium.org, thakis@chromium.org
BUG=123026
TEST=remove from DEPS and .DEPS.git, delete HKCU\Software\Cygnus Solutions\... and build successfully.

Review URL: https://codereview.chromium.org/149063008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248802 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248803 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248803