compiler: remove AbiDatas

These were a way to ensure hashes were stable over time for ExternAbi,
but simply hashing the strings is more stable in the face of changes.
As a result, we can do away with them.

compiler/rustc_ast_lowering/src/stability.rs

@@ -8,10 +8,10 @@ use rustc_span::symbol::sym;
 use rustc_span::{Span, Symbol};
 
 pub(crate) fn enabled_names(features: &rustc_feature::Features, span: Span) -> Vec<&'static str> {
-    rustc_abi::AbiDatas
-        .iter()
-        .filter(|data| extern_abi_enabled(features, span, data.abi).is_ok())
-        .map(|d| d.name)
+    ExternAbi::ALL_VARIANTS
+        .into_iter()
+        .filter(|abi| extern_abi_enabled(features, span, **abi).is_ok())
+        .map(|abi| abi.as_str())
         .collect()
 }