Use junit-hostdex instead of core-junit-hostdex/junit4-target-hostdex
Use junit-hostdex instead of core-junit-hostdex/junit4-target-hostdex

A recent change in external/junit changes junit-hostdex so it
includes all JUnit classes not just the ones not in
core-junit-hostdex and not in junit4-target-hostdex. This change
updates this project to use junit-hostdex instead of either of
or even both of the other two.

Bug: 30188076
Test: make checkbuild and art/tools/run-libcore-tests.sh '--mode=host' '--variant=X32'
Change-Id: Ifa4a5e68be2aa937cf1712255dbddcc9b6e11d72

google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt