Remove system-headers, minimize unwanted warnings.

* If necessary, use --header-filter to select warnings
  in owned header files for each module.

Change-Id: I5a2a52a4f78661b60a8375fbcc46bd5bad92ae60
Test: make with WITH_TIDY=1

cmds/idmap2/Android.bp

@@ -56,9 +56,6 @@ cc_defaults {
         "-readability-redundant-access-specifiers",
         "-readability-uppercase-literal-suffix",
     ],
-    tidy_flags: [
-        "-system-headers",
-    ],
 }
 
 cc_library {