[jOOQ/jOOQ#9196] Fix date arithmetic in Expression

Fixes chained invocations of `Field#add()` on a DATE or TIMESTAMP field,
where the problem was that `Expression` had an override of `Field#add()`
which didn't match up with its implementation of `accept()`.

jOOQ/src/main/java/org/jooq/impl/Expression.java

@@ -133,16 +133,6 @@ final class Expression<T> extends AbstractField<T> {
         this.arguments = Tools.combine(lhs, rhs);
     }
 
-    @Override
-    public final Field<T> add(Field<?> value) {
-        if (operator == ExpressionOperator.ADD) {
-            rhs.add(value);
-            return this;
-        }
-
-        return super.add(value);
-    }
-
     @Override
     public final Field<T> mul(Field<? extends Number> value) {
         if (operator == ExpressionOperator.MULTIPLY) {