Fix dependencies of packages that target earlier releases

A previous change added legacy-android-test as a static dependency to
all packages that build against the current, test_current or
system_current and failed to compile when the junit and android.test
classes were removed from the API. Unfortunately, those changes did not
take into account that some of those packages target earlier API
versions and so will always have the classes available at runtime.

Bug: 30188076
Test: make checkbuild and ran a sample of tests
Change-Id: I78863420bcfd401b63b35ef5a9252024d1550b27
Signed-off-by: Adrian DC <radian.dc@gmail.com>