Change Vec examples to not assert exact capacity except where it is guaranteed

[Nemo157]

It was brought up on discord that the Vec::into_boxed_slice example contradicted the Vec::with_capacity docs in that the returned Vec might have more capacity than requested.

So, to reduce confusion change all the assert_eq!(vec.capacity(), _) to assert!(vec.capacity() >= _), except in 4 examples that have guaranteed capacities: Vec::from_raw_parts, Vec::from_raw_parts_in, Vec::<()>::with_capacity,Vec::<(), _>::with_capacity_in.

[rustbot]

r? @joshtriplett

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[joshtriplett]

@bors r+ rollup

[bors]

📌 Commit a9cb482 has been approved by joshtriplett

It is now in the queue for this repository.