Re-enable adaptive allocator

Recent Netty versions have improved the adaptive allocator, and we shouldn't be seeing the OOM issues others were noticing before. Let's re-enable it.

As for the buffer resizing issue, the upstream issue netty/netty#14912 is long fixed. I think we *should* pre-allocate the buffers beforehand much more aggressively, but that has to be future work.

proxy/src/main/java/com/velocitypowered/proxy/Velocity.java

@@ -47,11 +47,6 @@ public class Velocity {
       System.setProperty("io.netty.native.workdir", System.getProperty("velocity.natives-tmpdir"));
     }
 
-    // Restore allocator used before Netty 4.2 due to oom issues with the adaptive allocator
-    if (System.getProperty("io.netty.allocator.type") == null) {
-      System.setProperty("io.netty.allocator.type", "pooled");
-    }
-
     // Disable the resource leak detector by default as it reduces performance. Allow the user to
     // override this if desired.
     if (!VelocityProperties.hasProperty("io.netty.leakDetection.level")) {