Remove unused libbacktrace library.

Bug: 120606663

Test: Builds.
Change-Id: I733defd03670b01a30c4be5742498d62db7a9b6b
diff --git a/tests/unit/Android.bp b/tests/unit/Android.bp
index 96ea761..7b23255 100644
--- a/tests/unit/Android.bp
+++ b/tests/unit/Android.bp
@@ -10,7 +10,6 @@
     name: "FrameworksNetTests-jni-defaults",
     jni_libs: [
         "ld-android",
-        "libbacktrace",
         "libbase",
         "libbinder",
         "libbpf",