Versions before v0.9.0 (which didn't even support hinting with QtWebEngine!)
used to write QtWebEngine data to:
~/.local/share/qutebrowser/qutebrowser/QtWebEngine/Default
~/.cache/qutebrowser/qutebrowser/QtWebEngine/Default
In v0.9.0 this was changed to:
~/.local/share/qutebrowser/webengine
~/.cache/qutebrowser/webengine
Now we don't try to migrate data from the old location anymore.