Remove implementations of the `VariableOutput` trait #1361

Job	Run time
set-msrv / set-msrv	4s
minimal-versions / minimal-versions	33s
test (1.85.0)	31s
build (stable, thumbv7em-none-eabi)	42s
test (stable)	29s
build (stable, wasm32-unknown-unknown)	24s
build (1.85.0, wasm32-unknown-unknown)	26s
build (1.85.0, thumbv7em-none-eabi)	28s
	3m 37s

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