[3.14] gh-127146: Emscripten: Don't need to avoid unpaired surrogate anymore (GH-136707) (#136717)

This might have been fixed by gh-136624, or by some Emscripten change.
In any case, it no longer seems to be needed.
(cherry picked from commit dcd27aace180737adaddc79c00c181816fc6e162)

Co-authored-by: Hood Chatham <roberthoodchatham@gmail.com>