[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>

searx/engines/google.py

@@ -112,7 +112,8 @@ filter_mapping = {0: 'off', 1: 'medium', 2: 'high'}
 # ------------------------
 
 # google results are grouped into <div class="g ..." ../>
-results_xpath = '//div[contains(@class, "g")]'
+results_xpath = '//div[@id="search"]//div[contains(@class, "g ")]'
+results_xpath_mobile_ui = '//div[contains(@class, "g ")]'
 
 # google *sections* are no usual *results*, we ignore them
 g_section_with_header = './g-section-with-header'
@@ -336,7 +337,12 @@ def response(resp):
                 logger.error(e, exc_info=True)
 
     # parse results
-    for result in eval_xpath_list(dom, results_xpath):
+
+    _results_xpath = results_xpath
+    if use_mobile_ui:
+        _results_xpath = results_xpath_mobile_ui
+
+    for result in eval_xpath_list(dom, _results_xpath):
 
         # google *sections*
         if extract_text(eval_xpath(result, g_section_with_header)):