Don't send a huge number of unneeded wxChildFocusEvents.

Don't send a huge number of unneeded wxChildFocusEvents.

wxControlContainer::SetLastFocus() propagated wxChildFocusEvent explicitly to
its parent but this is not needed because wxChildFocusEvents propagate by
default, being derived from wxCommandEvent. And doing it again resulted in the
total number of events increasing exponentially with the depth of the window
hierarchy and real performance problems due to processing all of them.

Closes #14310.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71559 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775