Modify Syzygy buildbot to use DEPS.syzygy.
Modify Syzygy buildbot to use DEPS.syzygy.

This allows Syzygy to track different dependencies than Sawbuck/Sawdust, which currently all share a repo.

BUG=

Review URL: https://codereview.chromium.org/155933002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@249068 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build