C++17 is the default now.

Test: builds
Change-Id: I4a9741ae2ccf48d9db7aa7dd42ab66f9750f165d
diff --git a/sigchainlib/Android.bp b/sigchainlib/Android.bp
index a151d7a..1d5ec2b 100644
--- a/sigchainlib/Android.bp
+++ b/sigchainlib/Android.bp
@@ -16,7 +16,6 @@
 
 cc_library {
     name: "libsigchain",
-    cpp_std: "gnu++17",
 
     host_supported: true,
     defaults: ["art_defaults"],