Remove a flaky test

tests/compile-fail/stacked_borrows/track_id.rs

@@ -1,19 +0,0 @@
-// compile-flags: -Zmiri-track-pointer-tag=1372
-// do not run on anything but x86_64 linux, because minor libstd changes can change the borrow stack ids
-// only-x86_64
-// only-linux
-
-use std::mem;
-
-fn main() {
-    let mut target = 42;
-    // Make sure we cannot use a raw-tagged `&mut` pointing to a frozen location.
-    // Even just creating it unfreezes.
-    let raw = &mut target as *mut _; // let this leak to raw
-    let reference = unsafe { &*raw }; // freeze
-    let ptr = reference as *const _ as *mut i32; // raw ptr, with raw tag
-    let _mut_ref: &mut i32 = unsafe { mem::transmute(ptr) }; // &mut, with raw tag
-    //~^ ERROR disabling item [SharedReadOnly for <1372>] for tag Some(<untagged>)
-    // Now we retag, making our ref top-of-stack -- and, in particular, unfreezing.
-    let _val = *reference;
-}