Emscripten: Do not define BINARYEN_TRAP_MODE='clamp'
It is not supported in Emscripten's `latest-upstream` LLVM backend,
and doesn't seem necessary in the `latest` backend either.
It was initially added in #22857 to solve a compilation error with the latter.
Part of #30270.
(cherry picked from commit 63544e6b02e42935b9f23ade6ff14a6731abe72d)