Remove unnecessary min_specialization after bootstrap

These crates all needed specialization for `newtype_index!`, which will no
longer be necessary when the current nightly eventually becomes the next
bootstrap compiler.

compiler/rustc_hir_analysis/src/lib.rs

@@ -67,7 +67,7 @@ This API is completely unstable and subject to change.
 #![feature(is_sorted)]
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
-#![feature(min_specialization)]
+#![cfg_attr(bootstrap, feature(min_specialization))]
 #![feature(never_type)]
 #![feature(lazy_cell)]
 #![feature(slice_partition_dedup)]