JS: Simplify call graph metric

javascript/ql/src/meta/analysis-quality/CallGraphQuality.qll

@@ -173,12 +173,20 @@ SourceNode nodeLeadingToInvocation() {
   )
 }
 
+/**
+ * Holds if there is a call edge `invoke -> f` between a relevant invocation
+ * and a relevant function.
+ */
+predicate relevantCall(RelevantInvoke invoke, RelevantFunction f) {
+  FlowSteps::calls(invoke, f)
+}
+
 /**
  * A call site that can be resolved to a function in the same project.
  */
 class ResolvableCall extends RelevantInvoke {
   ResolvableCall() {
-    FlowSteps::calls(this, _)
+    relevantCall(this, _)
     or
     this = resolvableCallback().getAnInvocation()
   }

javascript/ql/src/meta/analysis-quality/ResolvableCallCandidates.ql

@@ -11,4 +11,4 @@
 import javascript
 import CallGraphQuality
 
-select projectRoot(), count(NonExternalCall call)
+select projectRoot(), count(RelevantInvoke call)

javascript/ql/src/meta/analysis-quality/ResolvableCallRatio.ql

@@ -11,4 +11,4 @@
 import javascript
 import CallGraphQuality
 
-select projectRoot(), 100.0 * count(ResolvableCall call) / count(NonExternalCall call).(float)
+select projectRoot(), 100.0 * count(ResolvableCall call) / count(RelevantInvoke call).(float)