ninja: delete an obsolete comment about a removed hack
ninja: delete an obsolete comment about a removed hack

Due to an earlier restat change, we no longer need a Chrome-specific
hack for lastchange.
I accidentally deleted the code related to this comment in my previous
commit.

Review URL: http://codereview.chromium.org/9210005
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google