vec in-place-drop: avoid creating an intermediate slice

[hkBst]

Avoids clippy warning:

warning: implicitly casting the result of `from_raw_parts_mut` to `*mut [T]`
--> library/alloc/src/vec/in_place_drop.rs:25:32
|
25 | ptr::drop_in_place(slice::from_raw_parts_mut(self.inner, self.len()));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace_with: `core::ptr::slice_from_raw_parts_mut(self.inner, self.len())`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_slice_from_raw_parts
= note: `-W clippy::cast-slice-from-raw-parts` implied by `-W clippy::suspicious`
= help: to override `-W clippy::suspicious` add `#[allow(clippy::cast_slice_from_raw_parts)]`

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[tgross35]

@bors r+ rollup

[bors]

📌 Commit 47798e2 has been approved by tgross35

It is now in the queue for this repository.