Remove unused variable.

Test: Builds with -Wunused-variable
Change-Id: I201d15d1a61f55ccdf81cdc3d8ee4fe349455dcd
diff --git a/tests/binder_test.cpp b/tests/binder_test.cpp
index 359a28f..ad04ed3 100644
--- a/tests/binder_test.cpp
+++ b/tests/binder_test.cpp
@@ -164,7 +164,6 @@
 constexpr int BASE_UID = AID_USER_OFFSET * 5;
 
 static const std::string NO_SOCKET_ALLOW_RULE("! owner UID match 0-4294967294");
-static const std::string ESP_ALLOW_RULE("esp");
 
 static const in6_addr V6_ADDR = {
         {// 2001:db8:cafe::8888