[wasm][cleanup] Remove useless and wrong comment

The amortized cost of a single invocation is actually O(1), not O(n).
But this whole comment is needless anyway, so just remove it.

R=ahaas@chromium.org
NOTRY=true

Change-Id: Icffaedcd784584b1676cd7ed323555177a62d63e
Reviewed-on: https://chromium-review.googlesource.com/997812Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52395}

src/wasm/wasm-objects.h

@@ -175,10 +175,10 @@ class WasmMemoryObject : public JSObject {
                                 WASM_MEMORY_OBJECT_FIELDS)
 #undef WASM_MEMORY_OBJECT_FIELDS
 
-  // Add an instance to the internal (weak) list. amortized O(n).
+  // Add an instance to the internal (weak) list.
   static void AddInstance(Isolate* isolate, Handle<WasmMemoryObject> memory,
                           Handle<WasmInstanceObject> object);
-  // Remove an instance from the internal (weak) list. O(n).
+  // Remove an instance from the internal (weak) list.
   static void RemoveInstance(Isolate* isolate, Handle<WasmMemoryObject> memory,
                              Handle<WasmInstanceObject> object);
   uint32_t current_pages();