Remove unused a.t.InstrumentationCoreTestRunner

The only usage of this was in the unused
cts/tests/vm-tests-tf/AndroidManifest.xml which was deleted in
https://android-review.googlesource.com/#/c/418900/.

Bug: 30188076
Test: make checkbuild
Change-Id: I96f3586a7017f4cd14fa31207e0fff19c92f0de4