MIPS: Remove the HValueOf instruction.

Port r18905 (88f14cd3)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/130803012

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18930 ce2b1a6d-e550-0410-aec6-3dcde31c8c00