Remove proxies from --harmony switch for M38, because problems

They can still be activated separately using the --harmony-proxies switch,
but are no longer implied by Chrome's "Experimental JavaScript" option.

R=yangguo@chromium.org
BUG=
LOG=Y

Review URL: https://codereview.chromium.org/453903002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22990 ce2b1a6d-e550-0410-aec6-3dcde31c8c00