rustc: Stop adding the Send bound implicitly

This commit removes implicitly adding the Send bound to ~Trait objects and
procedure types. It will now be manually required to specify that a procedure
or trait must be send-able.

Closes #10296

Author: alexcrichton

src/librustc/middle/typeck/astconv.rs

@@ -850,15 +850,12 @@ fn conv_builtin_bounds(tcx: &ty::ctxt, ast_bounds: &Option<OwnedSlice<ast::TyPar
             }
             builtin_bounds
         },
-        // ~Trait is sugar for ~Trait:Send.
-        (&None, ty::UniqTraitStore) => {
-            let mut set = ty::EmptyBuiltinBounds(); set.add(ty::BoundSend); set
-        }
         // &'static Trait is sugar for &'static Trait:'static.
         (&None, ty::RegionTraitStore(ty::ReStatic)) => {
             let mut set = ty::EmptyBuiltinBounds(); set.add(ty::BoundStatic); set
         }
-        // &'r Trait is sugar for &'r Trait:<no-bounds>.
-        (&None, ty::RegionTraitStore(..)) => ty::EmptyBuiltinBounds(),
+        // No bounds are automatically applied for &'r Trait or ~Trait
+        (&None, ty::RegionTraitStore(..)) |
+        (&None, ty::UniqTraitStore) => ty::EmptyBuiltinBounds(),
     }
 }