Redefine `NodeIndex` as a `newtype_index!`.

This commit removes the custom index implementation of `NodeIndex`,
which probably predates `newtype_index!`.

As well as eliminating code, it improves the debugging experience,
because the custom implementation had the property of being incremented
by 1 (so it could use `NonZeroU32`), which was incredibly confusing if
you didn't expect it.

For some reason, I also had to remove an `unsafe` block marker from
`from_u32_unchecked()` that the compiler said was now unnecessary.

0 files changed, 0 insertions, 0 deletions