Remove usage of specialization from rustc_borrowck

compiler/rustc_borrowck/src/facts.rs

@@ -213,8 +213,32 @@ trait FactCell {
     fn to_string(&self, location_table: &LocationTable) -> String;
 }
 
-impl<A: Debug> FactCell for A {
-    default fn to_string(&self, _location_table: &LocationTable) -> String {
+impl FactCell for BorrowIndex {
+    fn to_string(&self, _location_table: &LocationTable) -> String {
+        format!("{self:?}")
+    }
+}
+
+impl FactCell for Local {
+    fn to_string(&self, _location_table: &LocationTable) -> String {
+        format!("{self:?}")
+    }
+}
+
+impl FactCell for MovePathIndex {
+    fn to_string(&self, _location_table: &LocationTable) -> String {
+        format!("{self:?}")
+    }
+}
+
+impl FactCell for PoloniusRegionVid {
+    fn to_string(&self, _location_table: &LocationTable) -> String {
+        format!("{self:?}")
+    }
+}
+
+impl FactCell for RegionVid {
+    fn to_string(&self, _location_table: &LocationTable) -> String {
         format!("{self:?}")
     }
 }

compiler/rustc_borrowck/src/lib.rs

@@ -7,7 +7,6 @@
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]