Remove the widgetsnanobrowser example

This example hasn't been touched since we imported QtWebKit examples.
If we need to have a more test-purpose widgets browser in the future,
we can dig it back from the history.

Change-Id: Icee9bd7f09827a97b33c6783b87311e331d963b1
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>