Suppress clang 7.0 warnings.

* Remove unrecognized -Wno-extended-offsetof.

Test: checkbuild
Change-Id: I21f6aed8fbafa2b4545a8d7fcd1c586e36452c3d
(cherry-picked from goog/pi-dev f7036c2cddf21dbfb871f43f660cbb131bb0bd52)
diff --git a/Android.bp b/Android.bp
index 6350262..a07fdbb 100644
--- a/Android.bp
+++ b/Android.bp
@@ -23,7 +23,6 @@
 cc_defaults {
     name: "nos_proto_defaults",
     cflags: [
-        "-Wno-extended-offsetof",
         "-Wno-unused-parameter",
     ],
 }