cleanup player death event adventure logic (#10095)

There was a TODO left there regarding the translated death
message being used by plugins to identify the cause of death. This
should be mitigated now because the LegacyComponentSerializer default
implemenation uses our custom flattener which renders vanilla
translatable components to their English representation.

patches/api/0175-PlayerDeathEvent-getItemsToKeep.patch

@@ -8,19 +8,19 @@ Exposes a mutable array on items a player should keep on death
 Example Usage: https://gist.github.com/aikar/5bb202de6057a051a950ce1f29feb0b4
 
 diff --git a/src/main/java/org/bukkit/event/entity/PlayerDeathEvent.java b/src/main/java/org/bukkit/event/entity/PlayerDeathEvent.java
-index 27909044c0c136acde18d64f14e84de932ba1045..ed7ede83507c052e05afffea78600b16439590dd 100644
+index 59b84a0e07ddc214a419d5b59ab3a86c5ab63b78..3ce76cfb09f6f5eb55e950843bdd846b2b561116 100644
 --- a/src/main/java/org/bukkit/event/entity/PlayerDeathEvent.java
 +++ b/src/main/java/org/bukkit/event/entity/PlayerDeathEvent.java
-@@ -36,7 +36,6 @@ public class PlayerDeathEvent extends EntityDeathEvent {
+@@ -37,7 +37,6 @@ public class PlayerDeathEvent extends EntityDeathEvent {
      }
-     // Paper end
+     // Paper end - adventure
  
 -    @Deprecated // Paper
      public PlayerDeathEvent(@NotNull final Player player, @NotNull final List<ItemStack> drops, final int droppedExp, @Nullable final String deathMessage) {
          this(player, drops, droppedExp, 0, deathMessage);
      }
 @@ -56,6 +55,41 @@ public class PlayerDeathEvent extends EntityDeathEvent {
-         this.adventure$deathMessage = deathMessage != null ? net.kyori.adventure.text.serializer.legacy.LegacyComponentSerializer.legacySection().deserialize(deathMessage) : null; // Paper
+         this.deathMessage = net.kyori.adventure.text.serializer.legacy.LegacyComponentSerializer.legacySection().deserializeOrNull(deathMessage); // Paper
      }
  
 +    @Deprecated // Paper