stop zeroing the drop flag in drop glue

this is only going to cover up real bugs, as it's not part of the model
used to prevent multiple destructor calls

src/librustc/middle/trans/glue.rs

@@ -423,7 +423,6 @@ pub fn trans_struct_drop_flag(bcx: @mut Block, t: ty::t, v0: ValueRef, dtor_did:
             bcx = drop_ty(bcx, llfld_a, fld.mt.ty);
         }
 
-        Store(bcx, C_u8(0), drop_flag);
         bcx
     }
 }