MIPS: Remove keyed_store_calling convention and friends.

Port r22706 (aae2de24)

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/429893006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22724 ce2b1a6d-e550-0410-aec6-3dcde31c8c00