Remove `ExactSizeIterator` constraint from `SimpleSmt::with_leaves()` #807

Job	Run time
rustfmt	12s
Test stable on ubuntu with --features default,std,serde	48s
Clippy with --features default,std,serde	25s
Test stable on ubuntu with --no-default-features	45s
Build stable on ubuntu with --no-default-features --target wasm32-unknown-unknown	24s
Clippy with --no-default-features	18s
Test nightly on ubuntu with --features default,std,serde	47s
Build nightly on ubuntu with --no-default-features --target wasm32-unknown-unknown	25s
Test nightly on ubuntu with --no-default-features	47s
	4m 51s

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