Remove ExpressionLanguage reference for 2.3 version

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3 only
| Fixed tickets | 

Remove "Using Expressions for Complex Security Restrictions" section using ExpressionLanguage in 2.3 version.

ExpressionLanguage is a 2.4 feature.