gn2bp: properly apply -frtti

-frtti is already in the flags. No need to use additional_args.

Test: //components/cronet/android:cronet
Change-Id: I20b4ae24b6dc09ffba3ec41dbf192ef11f7b4c6a
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index b222d6f..cdee102 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -129,7 +129,6 @@
         }),
     ],
     'cronet_aml_components_cronet_android_cronet': [
-        ('rtti', True),
         ('cppflags', {
             # TODO: figure out if there is no way around this and if this is
             # allowed for platform code.
@@ -1139,6 +1138,8 @@
         module.cpp_std = flag[len('-std='):]
       if '-isystem' in flag:
         local_include_dirs_set.add(flag[len('-isystem../../'):])
+      if '-frtti' in flag:
+        module.rtti = True
 
     # Adding local_include_dirs is necessary due to source_sets / filegroups
     # which do not properly propagate include directories.