Remove (lots of) dead code

Found with https://github.com/est31/warnalyzer.

Dubious changes:
- Is anyone else using rustc_apfloat? I feel weird completely deleting
  x87 support.
- Maybe some of the dead code in rustc_data_structures, in case someone
  wants to use it in the future?
- Don't change rustc_serialize

  I plan to scrap most of the json module in the near future (see
  https://github.com/rust-lang/compiler-team/issues/418) and fixing the
  tests needed more work than I expected.

TODO: check if any of the comments on the deleted code should be kept.

compiler/rustc_middle/src/mir/mod.rs

@@ -379,24 +379,6 @@ impl<'tcx> Body<'tcx> {
         }
     }
 
-    /// Returns an iterator over all temporaries.
-    #[inline]
-    pub fn temps_iter<'a>(&'a self) -> impl Iterator<Item = Local> + 'a {
-        (self.arg_count + 1..self.local_decls.len()).filter_map(move |index| {
-            let local = Local::new(index);
-            if self.local_decls[local].is_user_variable() { None } else { Some(local) }
-        })
-    }
-
-    /// Returns an iterator over all user-declared locals.
-    #[inline]
-    pub fn vars_iter<'a>(&'a self) -> impl Iterator<Item = Local> + 'a {
-        (self.arg_count + 1..self.local_decls.len()).filter_map(move |index| {
-            let local = Local::new(index);
-            self.local_decls[local].is_user_variable().then_some(local)
-        })
-    }
-
     /// Returns an iterator over all user-declared mutable locals.
     #[inline]
     pub fn mut_vars_iter<'a>(&'a self) -> impl Iterator<Item = Local> + 'a {