Remove an experimental `js` feature #1870

Job	Run time
pre_job	3s
linux-cross (aarch64-unknown-linux-musl, stable)	4m 18s
linux-cross (i686-unknown-linux-musl, stable)	3m 39s
linux-cross (armv7-unknown-linux-musleabihf, stable)	4m 10s
linux-cross (armv5te-unknown-linux-musleabi, --no-default-features, stable)	7m 51s
linux-cross (mips-unknown-linux-musl, --no-default-features, 1.72.1, +1.72.1)	4m 41s
linux-cross (mipsel-unknown-linux-musl, --no-default-features, 1.72.1, +1.72.1)	4m 39s
	29m 21s

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