Remove stale dependency on dx.

It causes trouble if we try to switch test builds to "unbundled" mode
(in the Soong sense, i.e. a build not intended to create any system
images), because dx is disabled there.

Test: rm -rf out && art/test/testrunner/run_build_test_target.py art-linux-bionic-x64
Test: m nothing
Test: art/tools/buildbot-build.sh
Bug: 157549171
Change-Id: I500e5e6cf2b749e12288fd22efc7bfb79c76dfd7
diff --git a/test/Android.run-test.mk b/test/Android.run-test.mk
index 64a177f..aa6c43d 100644
--- a/test/Android.run-test.mk
+++ b/test/Android.run-test.mk
@@ -19,7 +19,6 @@
 
 # Dependencies for actually running a run-test.
 TEST_ART_RUN_TEST_DEPENDENCIES := \
-  $(HOST_OUT_EXECUTABLES)/dx \
   $(HOST_OUT_EXECUTABLES)/d8 \
   $(HOST_OUT_EXECUTABLES)/hiddenapi \
   $(HOST_OUT_EXECUTABLES)/jasmin \