docs(audience): soften Identity.Get comment

"e.g. GDPR deletion" was too specific to one use case. The real
contract is "returns-without-creating", which any call site should
reason about on its own merits. Reworded to describe the contract,
not a caller.

Author: ImmutableJeffrey

src/Packages/Audience/Runtime/Core/Identity.cs

@@ -18,8 +18,8 @@ internal sealed class Identity
         private static readonly object _sync = new object();
 
         // Returns the existing anonymous ID, or null if none exists. Never
-        // creates one — use for call sites that must not implicitly register
-        // a new ID (e.g. GDPR deletion).
+        // creates one — for call sites that must not register a new ID as
+        // a side-effect.
         internal static string? Get(string persistentDataPath)
         {
             if (_cachedId != null) return _cachedId;