[cfe] Remove unknownFunction

The `unknownFunction` marker object was used to indicate a type of a
function that accepts an unspecified amount of arguments. The uses of
the marker object in the CFE are already replaced by
InvocationTargetType and its subtypes. This CL simply removes the
object itself, which is no longer in use.

Change-Id: I48fe53460d1f96f4fee0a91fb1572e219fbd1502
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/387702
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/front_end/lib/src/type_inference/type_inference_engine.dart

@@ -344,8 +344,6 @@ abstract class TypeInferenceEngine {
 /// kernel objects.
 class TypeInferenceEngineImpl extends TypeInferenceEngine {
   final Benchmarker? benchmarker;
-  final FunctionType unknownFunction =
-      new FunctionType(const [], const DynamicType(), Nullability.nonNullable);
 
   TypeInferenceEngineImpl(Instrumentation? instrumentation, this.benchmarker)
       : super(instrumentation);
@@ -364,11 +362,11 @@ class TypeInferenceEngineImpl extends TypeInferenceEngine {
     }
     if (benchmarker == null) {
       return new TypeInferrerImpl(this, uri, false, thisType, library,
-          assignedVariables, dataForTesting, unknownFunction);
+          assignedVariables, dataForTesting);
     }
     // Coverage-ignore(suite): Not run.
     return new TypeInferrerImplBenchmarked(this, uri, false, thisType, library,
-        assignedVariables, dataForTesting, benchmarker!, unknownFunction);
+        assignedVariables, dataForTesting, benchmarker!);
   }
 
   /// Creates a [TypeInferrer] object which is ready to perform type inference
@@ -386,11 +384,11 @@ class TypeInferenceEngineImpl extends TypeInferenceEngine {
     }
     if (benchmarker == null) {
       return new TypeInferrerImpl(this, uri, true, thisType, library,
-          assignedVariables, dataForTesting, unknownFunction);
+          assignedVariables, dataForTesting);
     }
     // Coverage-ignore(suite): Not run.
     return new TypeInferrerImplBenchmarked(this, uri, true, thisType, library,
-        assignedVariables, dataForTesting, benchmarker!, unknownFunction);
+        assignedVariables, dataForTesting, benchmarker!);
   }
 }
 

pkg/front_end/lib/src/type_inference/type_inferrer.dart

@@ -80,10 +80,6 @@ abstract class TypeInferrer {
 /// Concrete implementation of [TypeInferrer] specialized to work with kernel
 /// objects.
 class TypeInferrerImpl implements TypeInferrer {
-  /// Marker object to indicate that a function takes an unknown number
-  /// of arguments.
-  final FunctionType unknownFunction;
-
   final TypeInferenceEngine engine;
 
   final OperationsCfe operations;
@@ -132,8 +128,7 @@ class TypeInferrerImpl implements TypeInferrer {
       this.thisType,
       this.libraryBuilder,
       this.assignedVariables,
-      this.dataForTesting,
-      this.unknownFunction)
+      this.dataForTesting)
       : instrumentation = isTopLevel ? null : engine.instrumentation,
         typeSchemaEnvironment = engine.typeSchemaEnvironment,
         operations = new OperationsCfe(engine.typeSchemaEnvironment,
@@ -307,17 +302,8 @@ class TypeInferrerImplBenchmarked implements TypeInferrer {
     AssignedVariables<TreeNode, VariableDeclaration> assignedVariables,
     InferenceDataForTesting? dataForTesting,
     this.benchmarker,
-    FunctionType unknownFunctionNonNullable,
-  ) : impl = new TypeInferrerImpl(
-          engine,
-          uriForInstrumentation,
-          topLevel,
-          thisType,
-          library,
-          assignedVariables,
-          dataForTesting,
-          unknownFunctionNonNullable,
-        );
+  ) : impl = new TypeInferrerImpl(engine, uriForInstrumentation, topLevel,
+            thisType, library, assignedVariables, dataForTesting);
 
   @override
   AssignedVariables<TreeNode, VariableDeclaration> get assignedVariables =>