Knowledge Pad: Remove obsolete google gadgets

In https://lab.nexedi.com/nexedi/erp5/merge_requests/225 we realized google gadgets ( calendar, clock, maps and search ) no longer work since years, since they were hosted on google servers and they are longer hosted there.

Gadget framework is still working, our own gadgets (persons, worklists etc) too, in this merge request we just remove the gadgets that were hosted on google and not longer work.

I believe they were kind of example and we should not reimplement them or try to replace them.

/cc @gabriel @Tyagov @romain @kazuhiko

For more reference https://support.google.com/websearch/answer/2664197?hl=en
https://en.wikipedia.org/wiki/IGoogle https://en.wikipedia.org/wiki/Google_Gadgets