Remove an experimental `js` feature #1869

Job	Run time
pre_job	5s
linux-cross (aarch64-unknown-linux-musl, stable)	4m 14s
linux-cross (i686-unknown-linux-musl, stable)	3m 23s
linux-cross (armv7-unknown-linux-musleabihf, stable)	4m 4s
linux-cross (armv5te-unknown-linux-musleabi, --no-default-features, stable)	7m 43s
linux-cross (mips-unknown-linux-musl, --no-default-features, 1.72.1, +1.72.1)	4m 47s
linux-cross (mipsel-unknown-linux-musl, --no-default-features, 1.72.1, +1.72.1)	4m 45s
	29m 1s

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