Fix Bug In Struct Field Initialization

Fields were not given default values when a struct was declared
without initializers.

Also, cleanup code in the helper function for binary operations
on struct instances.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/P4Compiler/Types.swift

@@ -56,8 +56,6 @@ extension P4Struct: CompilableType {
       return .Error(maybe_parsed_type_id.error()!)
     }
 
-    print("Looking up \(parsed_type_id) in \(context.types)")
-
     if case .Ok(let found_type) = context.types.lookup(identifier: parsed_type_id),
       let found_struct_type = found_type as? P4Struct
     {