Disable GN.

This deletes the hooks and running GN to produce GYP files while the project is on hold.

BUG=350974
TBR=jam

Review URL: https://codereview.chromium.org/193053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256035 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256036 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256036