Drop bogus assert after r21552.

R=hpayer@chromium.org
BUG=v8:2070
LOG=N

Review URL: https://codereview.chromium.org/303493005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21554 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Cleanup GetPropertyWithCallback / SetPropertyWithCallback API

BUG=
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/305513004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21555 ce2b1a6d-e550-0410-aec6-3dcde31c8c00