MIPS: Revert r20974, r20991: Unify and simplify the FastCloneShallowArrayStub.

Port r21007 (3a5d22d)

Original commit message:
Due to Layout test redness.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/252023002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21024 ce2b1a6d-e550-0410-aec6-3dcde31c8c00