fix assets not being disposed when a content manager is disposed

src/SMAPI/Framework/Content/ContentCache.cs

@@ -119,7 +119,7 @@ namespace StardewModdingAPI.Framework.Content
         /// <param name="predicate">Matches the asset keys to invalidate.</param>
         /// <param name="dispose">Whether to dispose invalidated assets. This should only be <c>true</c> when they're being invalidated as part of a dispose, to avoid crashing the game.</param>
         /// <returns>Returns the removed keys (if any).</returns>
-        public IEnumerable<string> Remove(Func<string, Type, bool> predicate, bool dispose = false)
+        public IEnumerable<string> Remove(Func<string, Type, bool> predicate, bool dispose)
         {
             List<string> removed = new List<string>();
             foreach (string key in this.Cache.Keys.ToArray())

src/SMAPI/Framework/ContentManagers/BaseContentManager.cs

@@ -200,7 +200,7 @@ namespace StardewModdingAPI.Framework.ContentManagers
                     return true;
                 }
                 return false;
-            });
+            }, dispose);
 
             return removeAssetNames.Select(p => Tuple.Create(p.Key, p.Value));
         }