Reduce Symbol's interface slightly.

src/libsyntax_pos/symbol.rs

@@ -380,10 +380,6 @@ pub fn intern(string: &str) -> Self {
         with_interner(|interner| interner.intern(string))
     }
 
-    pub fn interned(self) -> Self {
-        with_interner(|interner| interner.interned(self))
-    }
-
     /// Gensyms a new `usize`, using the current interner.
     pub fn gensym(string: &str) -> Self {
         with_interner(|interner| interner.gensym(string))
@@ -502,7 +498,7 @@ pub fn intern(&mut self, string: &str) -> Symbol {
         name
     }
 
-    pub fn interned(&self, symbol: Symbol) -> Symbol {
+    fn interned(&self, symbol: Symbol) -> Symbol {
         if (symbol.0.as_usize()) < self.strings.len() {
             symbol
         } else {