Don't depend on [!Default; 0]: Default impl

[WaffleLapkin]

Description of Changes

There are plans to remove the unconditional [T; 0]: Default impl (where T doesn't necessarily implement Default) from the standard library (see rust-lang/rust#145457). That is a breaking change that would affect this crate.

This PR fixes this by removing a dependency on that impl.

API and ABI breaking changes

N/A

Expected complexity level and risk

1, there is no risk, the change is trivial.

Testing

No testing is required, <[T; 0]>::default() is always equivalent to [].

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[WaffleLapkin]

I will not sign the CLA, however this contribution is trivial enough that you can probably figure this out on your end ^^'

[bfops]

Thank you for making us aware of this! Since you mentioned you're not signing the CLA, I'll close this PR.