[cleanup] Remove unused _query_continue method.

QueryGenerator._query_continue method is no longer used since
b8060a7e8b8553f5beca6046809c7f99cc66a0c8 and can be removed.

rename _continue() method to continue_update and merge it
with _add_continues. Always return None with it instead of
False because the result is not important anymore.
This looks like a breaking change but it does not care.

Bug: T343204
Change-Id: I4eaa37f150f8c0d9a008419637b7c320385708b0
---
M pywikibot/data/api/_generators.py
1 file changed, 31 insertions(+), 22 deletions(-)

diff --git a/pywikibot/data/api/_generators.py b/pywikibot/data/api/_generators.py
index 1a30567..3090ef3 100644
--- a/pywikibot/data/api/_generators.py
+++ b/pywikibot/data/api/_generators.py
@@ -237,7 +237,6 @@
 
         parameters['indexpageids'] = True  # always ask for list of pageids
         self.continue_name = 'continue'
-        self.continue_update = self._continue
         # Explicitly enable the simplified continuation
         parameters['continue'] = True
         self.request = self.request_class(**kwargs)
@@ -476,24 +475,18 @@
 
         return None
 
-    def _query_continue(self) -> bool:
-        if all(key not in self.data[self.continue_name]
-               for key in self.continuekey):
-            pywikibot.log(
-                "Missing '{}' key(s) in ['{}'] value."
-                .format(self.continuekey, self.continue_name))
-            return True
+    def continue_update(self) -> None:
+        """Update query with continue parameters.
 
-        for query_continue_pair in self.data['query-continue'].values():
-            self._add_continues(query_continue_pair)
-        return False  # a new request with query-continue is needed
-
-    def _continue(self) -> bool:
-        self._add_continues(self.data['continue'])
-        return False  # a new request with continue is needed
-
-    def _add_continues(self, continue_pair) -> None:
-        for key, value in continue_pair.items():
+        .. versionadded:: 3.0
+        .. versionchanged:: 4.0
+           explicit return a bool value to be used in :meth:`generator`
+        .. versionchanged:: 6.0
+           always return *False*
+        .. versionchanged:: 8.4
+           return *None* instead of *False*.
+        """
+        for key, value in self.data['continue'].items():
             # query-continue can return ints (continue too?)
             if isinstance(value, int):
                 value = str(value)
@@ -653,10 +646,8 @@
             if self.continue_name not in self.data:
                 break
 
-            if self.continue_update():
-                break
-
-            del self.data  # a new request with (query-)continue is needed
+            self.continue_update()
+            del self.data  # a new request with continue is needed
 
     def result(self, data):
         """Process result data as needed for particular subclass."""

