Revert "Add flags to force or prevent setting of isolate.is_memory_constrained."

It introduces static initializers for the new "MAYBE_BOOL" kind of
flags, which is a no-no for Chrome. This has to be done differently.

TBR=danno@chromium.org

Review URL: https://codereview.chromium.org/23621044

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16736 ce2b1a6d-e550-0410-aec6-3dcde31c8c00