syntax: Don't add an extra space before the last comma...

...when printing struct update expressions.

src/libsyntax/print/pprust.rs

@@ -1153,7 +1153,6 @@ fn print_expr(s: ps, &&expr: @ast::expr) {
         commasep_cmnt(s, consistent, (*fields), print_field, get_span);
         match wth {
             Some(expr) => {
-                if vec::len((*fields)) > 0u { space(s.s); }
                 ibox(s, indent_unit);
                 word(s.s, ~",");
                 space(s.s);