Remove the websession-flatfile plugin configuration

Since Ied0f98fb websession-flatfile was replaced with websession broker.
This change removed leftover websession-flatfile configuration from
gerrit.config to avoid confusion.

Change-Id: I0d4d0a76641d5d69a5d86040a15ee44acffe45cf

setup_local_env/configs/gerrit.config

diff --git a/setup_local_env/configs/gerrit.config b/setup_local_env/configs/gerrit.config
index 8a176f2..20075d7 100644
--- a/setup_local_env/configs/gerrit.config
+++ b/setup_local_env/configs/gerrit.config
@@ -39,8 +39,6 @@
     directory = cache
 [plugins]
     allowRemoteAdmin = true
-[plugin "websession-flatfile"]
-    directory = $FAKE_NFS
 [plugin "events-kafka"]
     sendAsync = true
     bootstrapServers = $BROKER_HOST:$BROKER_PORT