Don't use llvm-defaults to build some tests.

It's not clear this was ever needed, it doesn't seem to make any
difference now, and these are the defaults for the obsolete renderscript
LLVM anyway, so... yeah.

This was noticed because it was causing some of our tests to be built as
C++11 rather than [the current default of] C++17.

Test: treehugger
Change-Id: I7d72b3fd58e9cf9a02048b0298eee845d19307f7

tests/Android.bp

@@ -741,7 +741,6 @@ cc_test_library {
     name: "libBionicLoaderTests",
     defaults: [
         "bionic_tests_defaults",
-        "llvm-defaults",
     ],
     srcs: [
         "atexit_test.cpp",