Remove unused SyntaxContext serialization impls

The implementations were wrong and unused.

Author: matthewjasper

src/librustc_metadata/decoder.rs

@@ -31,7 +31,7 @@ use syntax::ast::{self, Ident};
 use syntax::source_map;
 use syntax::symbol::{Symbol, sym};
 use syntax::ext::base::{MacroKind, SyntaxExtension};
-use syntax::ext::hygiene::{ExpnId, SyntaxContext};
+use syntax::ext::hygiene::ExpnId;
 use syntax_pos::{self, Span, BytePos, Pos, DUMMY_SP, NO_EXPANSION};
 use log::debug;
 
@@ -356,14 +356,6 @@ impl SpecializedDecoder<Ident> for DecodeContext<'_, '_> {
     }
 }
 
-impl SpecializedDecoder<SyntaxContext> for DecodeContext<'_, '_> {
-    fn specialized_decode(&mut self) -> Result<SyntaxContext, Self::Error> {
-        // FIXME(jseyfried): intercrate hygiene
-
-        Ok(SyntaxContext::empty())
-    }
-}
-
 impl<'a, 'tcx> SpecializedDecoder<Fingerprint> for DecodeContext<'a, 'tcx> {
     fn specialized_decode(&mut self) -> Result<Fingerprint, Self::Error> {
         Fingerprint::decode_opaque(&mut self.opaque)

src/librustc_metadata/encoder.rs

@@ -33,7 +33,6 @@ use syntax::attr;
 use syntax::source_map::Spanned;
 use syntax::symbol::{kw, sym, Ident};
 use syntax_pos::{self, FileName, SourceFile, Span};
-use syntax_pos::hygiene::SyntaxContext;
 use log::{debug, trace};
 
 use rustc::hir::{self, PatKind};
@@ -181,13 +180,6 @@ impl SpecializedEncoder<Ident> for EncodeContext<'tcx> {
     }
 }
 
-impl SpecializedEncoder<SyntaxContext> for EncodeContext<'tcx> {
-    fn specialized_encode(&mut self, _ctxt: &SyntaxContext) -> Result<(), Self::Error> {
-        // FIXME(jseyfried): intercrate hygiene
-        Ok(())
-    }
-}
-
 impl<'tcx> SpecializedEncoder<LocalDefId> for EncodeContext<'tcx> {
     #[inline]
     fn specialized_encode(&mut self, def_id: &LocalDefId) -> Result<(), Self::Error> {

src/libsyntax_pos/hygiene.rs

@@ -30,7 +30,6 @@ use crate::{Span, DUMMY_SP};
 use crate::edition::Edition;
 use crate::symbol::{kw, Symbol};
 
-use rustc_serialize::{UseSpecializedEncodable, UseSpecializedDecodable};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
 use std::fmt;
@@ -766,7 +765,3 @@ impl DesugaringKind {
         }
     }
 }
-
-impl UseSpecializedEncodable for SyntaxContext {}
-
-impl UseSpecializedDecodable for SyntaxContext {}