Do not generate classpaths proto for RuntimeI18n apex.

This is historically significant jar that must be kept in boot image
and platform's classpath config. Setting generate_classpaths_proto to
false guarantees the latter.

Bug: 191127295
Test: atest CtsClasspathsTestCases
Change-Id: I68b41d54203af68d1b0a966632cf44639b95cfae
diff --git a/apex/Android.bp b/apex/Android.bp
index 9826ae0..92fe1b1 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -67,6 +67,8 @@
 // The com.android.i18n's contribution to the bootclasspath.
 bootclasspath_fragment {
     name: "i18n-bootclasspath-fragment",
+    // b/191127295: keep i18n in platform's classpath config and boot image.
+    generate_classpaths_proto: false,
     contents: [
         "core-icu4j",
     ],