Fix sepolicy_tests on Mac 10.15

This is dlopened by sepolicy_tests, which uses embeds the python
interpreter built from our tree. That python interpreter links against
the shared version of libc++, so mixing it with this static copy was
causing segfaults on Mac 10.15 (but apparently not elsewhere).

Test: SANITIZE_HOST=address m treble_sepolicy_tests
Test: `m` on Mac 10.15
Change-Id: I31744acd018ea4c980c46a9979bbad17ae1c4f68
diff --git a/tests/Android.bp b/tests/Android.bp
index d27f333..926b5e4 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -11,7 +11,6 @@
-    stl: "libc++_static",
     sanitize: {
         never: true,