port r23689.

original commit message:

  Remove dead code for inline string hashing.

  This has become obsolete since hydrogenized StringAdd.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/545093002

Patch from Jing Bao <jing.bao@intel.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23714 ce2b1a6d-e550-0410-aec6-3dcde31c8c00