Don't just clear the persistent handle to NPObject function templates.

It's important to dispose the handle. This triggers the
CHECK(state() != NEAR_DEATH)

BUG=324225
TBR=marja@chromium.org

Review URL: https://codereview.chromium.org/95703002

git-svn-id: svn://svn.chromium.org/blink/trunk@162855 bbb929c8-8fbe-4397-9dbb-9b2b20218538