Drop obsolete HCheckMaps::HandleSideEffectsDominator().

In HCheckMaps::HandleSideEffectsDominator() we try to remove
redundant HCheckMaps instructions that are dominated by an
HStoreNamedField instruction with a transition. This is just
a special case of the check elimination and therefore obsolete
(it also gives some nice speedup since GVN just got cheaper).

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/261003002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21108 ce2b1a6d-e550-0410-aec6-3dcde31c8c00