Revert "Reland "MIPS: Add support for arch. revision 6 to mips32 port.""

This reverts commit r23050 for breaking runhooks on chromium.

See e.g.:
http://build.chromium.org/p/client.v8/builders/Chrome%20Linux%20Perf/builds/1438/steps/runhooks/logs/stdio

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/458983003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23053 ce2b1a6d-e550-0410-aec6-3dcde31c8c00