Remove potentially misleading realloc parenthetical
This parenthetical is problematic, because it suggests that the following is sound:
```rust
let layout = Layout:🆕:<[u8; 32]>();
let p1 = alloc(layout);
let p2 = realloc(p1, layout, 32);
if p1 == p2 {
p1.write([0; 32]);
dealloc(p1, layout);
} else {
dealloc(p2, layout);
}
```
At the very least, this isn't the case for [ANSI `realloc`](https://en.cppreference.com/w/c/memory/realloc)
> The original pointer `ptr` is invalidated and any access to it is undefined behavior (even if reallocation was in-place).
and [Windows `HeapReAlloc`](https://docs.microsoft.com/en-us/windows/win32/api/heapapi/nf-heapapi-heaprealloc) is unclear at best (`HEAP_REALLOC_IN_PLACE_ONLY`'s description may imply that the old pointer may be used if `HEAP_REALLOC_IN_PLACE_ONLY` is provided).
The conservative position is to just remove the parenthetical.
cc `@rust-lang/wg-unsafe-code-guidelines` `@rust-lang/wg-allocators`
56d540e057