Stop explicitly blocking Vanilla Method Profiler

At the time this was re-added, there was concern around how the JIT
would handle the system property that enabled it.

This shouldn't be a problem, and as such we no longer need to block
access to it.

The Vanilla Method Profiler will not provide much to most users however
there is no harm in providing it as an option. For most users, the
recommended and supported method for determining performance issues with
Paper will continue to be Timings.

Spigot-Server-Patches/Disable-Explicit-Network-Manager-Flushing.patch

@@ -12,7 +12,7 @@ flushing on the netty event loop, so it won't do the flush on the main thread.
 Renable flushing by passing -Dpaper.explicit-flush=true
 
 diff --git a/src/main/java/net/minecraft/server/NetworkManager.java b/src/main/java/net/minecraft/server/NetworkManager.java
-index b93a26e8f..3d32e0056 100644
+index b93a26e8..3d32e005 100644
 --- a/src/main/java/net/minecraft/server/NetworkManager.java
 +++ b/src/main/java/net/minecraft/server/NetworkManager.java
 @@ -0,0 +0,0 @@ public class NetworkManager extends SimpleChannelInboundHandler<Packet<?>> {