Do not use isErasedFunctionClass

This is broken, especially when dealing with impure functions.
I removed the function definition.

Author: natsukagami

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1514,15 +1514,6 @@ class Definitions {
    */
   def isContextFunctionClass(cls: Symbol): Boolean = scalaClassName(cls).isContextFunction
 
-  /** Is an erased function class.
-   *   - ErasedFunctionN for N > 0
-   *
-   * This should not be used for checking if a type is an erased function type. Use `isErasedFunctionType`.
-   * Only helpful if you have a `RefinedType(parent, nme.apply, mt)` and
-   * want to check if `parent` is an erased function class.
-   */
-  def isErasedFunctionClass(cls: Symbol): Boolean = scalaClassName(cls).isErasedFunction
-
   /** Is either FunctionXXL or  a class that will be erased to FunctionXXL
    *   - FunctionXXL
    *   - FunctionN for N >= 22

compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -621,7 +621,7 @@ class TypeErasure(sourceLanguage: SourceLanguage, semiEraseVCs: Boolean, isConst
       defn.FunctionType(0)
     case RefinedType(parent, nme.apply, refinedInfo) if parent.typeSymbol eq defn.PolyFunctionClass =>
       erasePolyFunctionApply(refinedInfo)
-    case RefinedType(parent, nme.apply, refinedInfo) if defn.isErasedFunctionClass(parent.typeSymbol) =>
+    case RefinedType(parent, nme.apply, refinedInfo) if defn.isErasedFunctionType(parent) =>
       eraseErasedFunctionApply(refinedInfo)
     case tp: TypeProxy =>
       this(tp.underlying)
@@ -887,7 +887,7 @@ class TypeErasure(sourceLanguage: SourceLanguage, semiEraseVCs: Boolean, isConst
         // because RefinedTypes <: TypeProxy and it would be caught by
         // the case immediately below
         sigName(this(tp))
-      case tp @ RefinedType(parent, nme.apply, refinedInfo) if defn.isErasedFunctionClass(parent.typeSymbol) =>
+      case tp @ RefinedType(parent, nme.apply, refinedInfo) if defn.isErasedFunctionType(parent) =>
         sigName(this(tp))
       case tp: TypeProxy =>
         sigName(tp.underlying)