Remove command "touch cmake".
Remove command "touch cmake".

Summary:
It is quite normal to rerun cmake to find new files through GLOB commands. This external command always forces cmake to run when you run make, meaning every make command takes longer than necessary. This PR removes the external command `touch CMakeLists.txt` and therefore leaves that decision up to the user when to rerun cmake and speeds up building when cmake is not required to rerun.
Closes https://github.com/caffe2/caffe2/pull/453

Reviewed By: Yangqing

Differential Revision: D4978919

Pulled By: bwasti

fbshipit-source-id: 0da4495b276a04f6ce46e1c8ceca0474b7573aa0

caffe2/caffe2,bwasti/caffe2,sf-wind/caffe2,davinwang/caffe2,xzturn/caffe2,Yangqing/caffe2,Yangqing/caffe2,bwasti/caffe2,pietern/caffe2,pietern/caffe2,Yangqing/caffe2,bwasti/caffe2,sf-wind/caffe2,davinwang/caffe2,sf-wind/caffe2,sf-wind/caffe2,Yangqing/caffe2,davinwang/caffe2,xzturn/caffe2,pietern/caffe2,xzturn/caffe2,bwasti/caffe2,xzturn/caffe2,Yangqing/caffe2,pietern/caffe2,bwasti/caffe2,sf-wind/caffe2,xzturn/caffe2,pietern/caffe2,davinwang/caffe2,davinwang/caffe2