drm_hwcomposer: Use the global default cpp_std.

Issues can arise when shared libraries with c++17 and c++20
loaded into the same process refer to the same global symbol
(usually std::string).

So avoid overriding the default cpp_std.

Bug: http://b/344590580
Signed-off-by: Elliott Hughes <enh@google.com>
[jstultz: Tweaked & expanded commit message]
Signed-off-by: John Stultz <jstultz@google.com>
Change-Id: I6bde2ab4d208c990103e6d303ec96a4969fa06ef
diff --git a/Android.bp b/Android.bp
index bc1a3b9..b547929 100644
--- a/Android.bp
+++ b/Android.bp
@@ -45,7 +45,6 @@
     cppflags: [
         "-DHWC2_INCLUDE_STRINGIFICATION",
         "-DHWC2_USE_CPP11",
-        "-std=c++17",
     ],
 
     relative_install_path: "hw",