SDL3's Emscripten video backend emulates SetWindowIcon by pointing the
page's <link rel="icon"> at a blob: URL of the encoded surface - a
reasonable desktop-icon mapping in general, but unwanted for an
embeddable widget where the host page already has its own favicon.
Verified via examples/basic: after this patch, no rel=icon link is
ever created/mutated while a table runs (previously a consumer had to
work around this with a MutationObserver reverting it every time).
