Revert "Auto merge of #133734 - scottmcm:lower-indexing-to-ptrmetadata, r=davidtwco,RalfJung"

This reverts commit b57d93d8b9, reversing
changes made to 0aeaa5eb22.

compiler/rustc_span/src/hygiene.rs

@@ -1163,9 +1163,6 @@ pub enum DesugaringKind {
     WhileLoop,
     /// `async Fn()` bound modifier
     BoundModifier,
-    /// Marks a `&raw const *_1` needed as part of getting the length of a mutable
-    /// slice for the bounds check, so that MIRI's retag handling can recognize it.
-    IndexBoundsCheckReborrow,
 }
 
 impl DesugaringKind {
@@ -1182,7 +1179,6 @@ impl DesugaringKind {
             DesugaringKind::ForLoop => "`for` loop",
             DesugaringKind::WhileLoop => "`while` loop",
             DesugaringKind::BoundModifier => "trait bound modifier",
-            DesugaringKind::IndexBoundsCheckReborrow => "slice indexing",
         }
     }
 }