Fix various warnings and minor issues

[hansjoachim]

• Fixed some more unused imports.
• Add parameters to a raw Map based on its usage.
• Removed some unused methods.
• Removed some unused fields. (Note that there's an optional commit which reduces visibility for an inner class in a test suite which made it possible to remove more unused methods and fields from it.)

I've left an open question regarding the unused local variable in PageHistoryResponder. There's a section of the code which spends time and effort assign a value to this variable, but it is never used for anything. I don't know what the intended behaviour here is, because it could be that the value should be used for something, or that the traversing cause some side-effects which are needed here, or potentially that the section is unnecessary and could be removed.