Remove "known_pagebreaks" from wxHtmlCell::AdjustPagebreak()

This parameter is not actually needed for any reasonable page breaking
algorithm, as it shouldn't care about any previous page breaks except
for the last one, which is already known as "*pagebreak - pageHeight" in
this function.

Removing it will allow to stop using wxArrayInt in the code using this
method and switch to an std::vector<int> instead.

This is not a backwards compatible change, but it seems that there is
very little code actually overriding this function (none could be found
in any open source repositories) and updating it should be as simple as
removing the now unneeded argument.

docs/changes.txt

@@ -69,6 +69,9 @@ Changes in behaviour which may result in build errors
 - wxHtmlDCRenderer::Render() arguments have changed, simply omit the ones not
   existing in the function signature any more to update the code using it.
 
+- wxHtmlCell::AdjustPagebreak() has lost its "known_pagebreaks" argument,
+  update your code if you override this method (you shouldn't be calling it).
+
 
 3.1.2: (released 2018-??-??)
 ----------------------------