Remove obsolete `cpp_std: "experimental"`.

This is why I prefer being specific...

Test: treehugger
Change-Id: Ia2f2f5a2a4499df8ab4041c573b0ef78aecbaf3c
diff --git a/tests/Android.bp b/tests/Android.bp
index bf78f50..5840018 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -17,7 +17,6 @@
 cc_defaults {
     name: "bionic_tests_defaults",
     host_supported: true,
-    cpp_std: "experimental",
     target: {
         darwin: {
             enabled: false,