Move libusb/BUILD.gn to the main tree.

This seems to be equivalent to the current gyp file.

Tested with:
  gn gen out/Release_gn
  ninja -C out/Release_gn libusb

BUG=

Review URL: https://codereview.chromium.org/226363005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@262447 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed