Revert "Send mapper events via context"

This reverts commit cec3f6a9.

As we discussed with Chris and Michael, it is more natural to keep the
flow of inputreader -> inputdevice -> inputmapper -> inputlistener
rather than having to come back to inputreader.

This also reduces the redundancy of having to mimic the inputlistener
interface inside the inputreader context.

Bug: 169866723
Test: atest inputflinger_tests
Change-Id: I4244947810d99ff40cfffaa34f6374aa18a238c6