Prune unnecessary symbols from read API

Bug: 328444881
Test: m
Change-Id: I3b730a6c3390a5d116d467f15f17e74a9096961d
diff --git a/tools/aconfig/aconfig_storage_read_api/Android.bp b/tools/aconfig/aconfig_storage_read_api/Android.bp
index 3fb6a53..946c00b 100644
--- a/tools/aconfig/aconfig_storage_read_api/Android.bp
+++ b/tools/aconfig/aconfig_storage_read_api/Android.bp
@@ -103,4 +103,7 @@
     ],
     min_sdk_version: "29",
     double_loadable: true,
+    cflags: [
+        "-fvisibility=hidden",
+    ],
 }