C#: Address review comments.

Author: michaelnebel

csharp/ql/src/Telemetry/ExternalApi.qll

@@ -19,9 +19,7 @@ private predicate isUninteresting(Callable c) {
   or
   // The data flow library uses read/store steps for properties, so we don't need to model them,
   // if both a getter and a setter exist.
-  exists(Property p | p = c.(Accessor).getDeclaration() |
-    exists(p.getSetter()) and exists(p.getGetter())
-  )
+  c.(Accessor).getDeclaration().(Property).isReadWrite()
 }
 
 /**

csharp/ql/src/utils/modeleditor/ModelEditor.qll

@@ -17,9 +17,7 @@ private predicate isUninteresting(Callable c) {
   or
   // The data flow library uses read/store steps for properties, so we don't need to model them,
   // if both a getter and a setter exist.
-  exists(Property p | p = c.(Accessor).getDeclaration() |
-    exists(p.getSetter()) and exists(p.getGetter())
-  )
+  c.(Accessor).getDeclaration().(Property).isReadWrite()
 }
 
 /**

csharp/ql/src/utils/modelgenerator/internal/CaptureModelsSpecific.qll

@@ -28,7 +28,7 @@ private predicate isHigherOrder(CS::Callable api) {
 }
 
 private predicate irrelevantAccessor(CS::Accessor a) {
-  exists(CS::Property p | p = a.getDeclaration() | exists(p.getSetter()) and exists(p.getGetter()))
+  a.getDeclaration().(CS::Property).isReadWrite()
 }
 
 /**