drop unnecessary warning disable flag

The previous commit cleaned up the code that needed this.

Bug: None
Test: local android build passes
Change-Id: Ife454147acc0e5f80d539577df4d5400c169ef28
diff --git a/Android.bp b/Android.bp
index 911e0fc..5052946 100644
--- a/Android.bp
+++ b/Android.bp
@@ -306,7 +306,6 @@
     defaults: ["libminijail_flags"],
 
     cflags: [
-        "-Wno-missing-field-initializers",
         "-DPRELOADPATH=\"/invalidminijailpreload.so\"",
     ],
     srcs: [