Remove a broken hawktracer annotation

[shssoichiro]

Some change seems to have occurred which causes this specific hawktracer
annotation to fail to compile. For the time being, remove it so that
hawktracer support can compile again.

[lu-zero]

What is the error?

[shssoichiro]

error[E0501]: cannot borrow `self` as immutable because previous closure requires unique access
   --> /home/runner/.cargo/git/checkouts/rav1e-14e16d25dd5cd9c0/de97f3b/src/scenechange/mod.rs:440:3
    |
440 |   #[hawktracer(cost_scenecut)]
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   |
    |   second borrow occurs here
    |   closure construction occurs here
    |   borrows occur due to use of `self` in closure
    |   first borrow later used by call
    |
    = note: this error originates in the attribute macro `hawktracer` (in Nightly builds, run with -Z macro-backtrace for more info)
    ```

[lu-zero]

Go for it.

[shssoichiro]

I wish there was a fix for it instead, but I think the issue is related to the fact that we use &mut self inside of the different threads in that function. So I think the only way to keep this annotation would be to completely rewrite how we thread things in this function, which probably requires reducing the threading effectiveness.