This covers all the remaining logic that explicitly
supported the deprecated ChooserTargetService flow (although
there may still be opportunities to further simplify any
design concessions that might have been made to accommodate
that support, e.g. [perhaps] support for heterogeneous
result types, etc.)
This is a pure refactoring to remove dead code that was
fully disabled in my recent cleanup CLs.
Test: build/presubmits (unused code)
Change-Id: Ic1d51a5e78afabad2bfb92093889d5de09c8da5f
07ab7af0d8