[fix] google engine: remove adds and fix mobile_ui selector

1. Fix issue reported in comment [1]
2. Fix XPath selector for the response of google's mobile UI, reported in
   comment [2]

[1] https://github.com/searxng/searxng/pull/777#issuecomment-1015121322
[2] https://github.com/searxng/searxng/pull/777#issuecomment-1015236238



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