[fix] drop engine dogpile

The engine was added in commit a4b07460 but now it shows new issues [1].

In the 90'th of the last century, dogpile had its own WEB index, but nowadays it
is a meta-search engine [2]

  Powered by technology, Dogpile returns all the best results from leading
  search engines including Google and Yahoo!

Using dogpile as an engine in SearXNG needs more investigation, a XPath solution
like we have is not enough.   It is questionable whether it still makes sense to
investigate more into a meta-search engine with a ReCAPTCHA in front.

With this patch the dogpile engine is removed

[1] https://github.com/searxng/searxng/issues/202
[2] https://www.dogpile.com/support/aboutus



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>