Remove references to sconsbuild.

scons hasn't been used in a long time.

BUG=305702
NOTRY=true

Review URL: https://codereview.chromium.org/26718002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228308 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228308