Remove unsafeReset doc from IntrusiveSharedPtr

Summary: `unsafeReset` was removed in as part of code review inD56043656 but the doc was not updated.

Differential Revision: D57358588

fbshipit-source-id: c6b4ec69f18535e22d8f4a29ed6a0446fada17f9

third-party/thrift/src/thrift/lib/cpp2/util/IntrusiveSharedPtr.h

@@ -64,11 +64,6 @@ namespace apache::thrift::util {
  * concurrent code, this might be impossible to ensure. This is why it's
  * considered unsafe.
  *
- * For unsafeReset(), the only remaining IntrusiveSharedPtr owner can release
- * (and therefore delete) the pointed-to object concurrently to a reset() call.
- * This is why it's considered unsafe. reset(std::nullptr_t) is provided
- * (without renaming) because this special case is always safe.
- *
  * The embedded control block has some implications on the capabilities:
  *   - No std::weak_ptr equivalent — the control block's lifetime is confined by
  *     the pointed-to object, which means that weak references are