Revert "Don't flush packet queue off main thread"

This reverts commit 1abd2bd279.

Sadly not gonna work due to server pings

Spigot-Server-Patches/0347-Handle-Excessive-Signs-in-Chunks-creating-large-pack.patch

@@ -1,4 +1,4 @@
-From 10a32d733a851719edd4c52fc25d673f1e3be4fd Mon Sep 17 00:00:00 2001
+From 57f98e2c510b576b4d3c94b12384b1bc4b6b5e33 Mon Sep 17 00:00:00 2001
 From: Aikar <aikar@aikar.co>
 Date: Sat, 2 Mar 2019 14:55:01 -0500
 Subject: [PATCH] Handle Excessive Signs in Chunks creating large packets
@@ -14,7 +14,7 @@ With further contributions from
 Co-Authored-by: Spottedleaf <spottedleaf@spottedleaf.dev>
 
 diff --git a/src/main/java/net/minecraft/server/NetworkManager.java b/src/main/java/net/minecraft/server/NetworkManager.java
-index b1dededc15..07e3ddb6e9 100644
+index b1dededc15..e966b6edcc 100644
 --- a/src/main/java/net/minecraft/server/NetworkManager.java
 +++ b/src/main/java/net/minecraft/server/NetworkManager.java
 @@ -158,19 +158,55 @@ public class NetworkManager extends SimpleChannelInboundHandler<Packet<?>> {
@@ -73,7 +73,7 @@ index b1dededc15..07e3ddb6e9 100644
 +
 +            this.packetQueue.addAll(packets); // atomic
 +        }
-+        if (MCUtil.isMainThread()) this.sendPacketQueue();
++        this.sendPacketQueue(); // ensure only one flush call is made
 +        // Paper end
      }