Always fully qualify the namespace to use in v8.h

Also, remove some unused methods.

BUG=none
R=dcarney@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/297223006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21487 ce2b1a6d-e550-0410-aec6-3dcde31c8c00