Tidy sanitizers, using instanceof not extends or a charpred where possible

ql/src/experimental/CWE-918/SSRF.qll

@@ -152,17 +152,13 @@ module ServerSideRequestForgery {
    * the binding function to run some validations for that field. If these binding functions returns
    * no error, then we consider these fields safe for SSRF.
    */
-  class BodySanitizer extends Sanitizer {
-    BodySanitizer() { this instanceof CheckedAlphanumericStructFieldRead }
-  }
+  class BodySanitizer extends Sanitizer instanceof CheckedAlphanumericStructFieldRead { }
 
   /**
    * The method Var of package validator is a sanitizer guard only if the check
    * of the error binding exists, and the tag to check is one of "alpha", "alphanum", "alphaunicode", "alphanumunicode", "number", "numeric".
    */
-  class ValidatorAsSanitizer extends SanitizerGuard {
-    ValidatorAsSanitizer() { this instanceof ValidatorVarCheck }
-
+  class ValidatorAsSanitizer extends SanitizerGuard instanceof ValidatorVarCheck {
     override predicate checks(Expr e, boolean branch) { this.checks(e, branch) }
   }
 }