Remove no-op setListener method from dumpstate listener

Bugreports using Bugreport API flow is stable, remove unused
legacy flow method: setListener.

* Remove DumpstateToken as it was only used by setListener.
* Remove listener_name_ and report_section_

Bug: 136066578
Test: Build and flash. Takes bugreport as expected.
Test: atest dumpstate_test
Test: `adb bugreport` works as expected.

Change-Id: I31d1795fa91275091950320c71f4cf085895e4e0