Remove unused aconfig

Remove nsd_expired_services_removal aconfig, since it is no
longer used.

Bug: 312669635
Test: m
Change-Id: I9b21b6102ed9a8160be3d853d44d9b051997d09e
diff --git a/common/flags.aconfig b/common/flags.aconfig
index ebfa13a..ad78d62 100644
--- a/common/flags.aconfig
+++ b/common/flags.aconfig
@@ -15,13 +15,6 @@
 }
 
 flag {
-  name: "nsd_expired_services_removal"
-  namespace: "android_core_networking"
-  description: "Remove expired services from MdnsServiceCache"
-  bug: "304649384"
-}
-
-flag {
   name: "set_data_saver_via_cm"
   namespace: "android_core_networking"
   description: "Set data saver through ConnectivityManager API"