Remove useless JFunctionX

We only need JFunctionX where X <= 2 for specialization.

Author: liufengyun

compiler/src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -1178,7 +1178,8 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
         val returnsUnit = field.meth.tpe.widenDealias.resultType.classSymbol == UnitClass
         if (returnsUnit)
           ctx.requiredClass(("dotty.runtime.function.JProcedure" + arity))
-        else ctx.requiredClass(("dotty.runtime.function.JFunction" + arity))
+        else if (arity <= 2) ctx.requiredClass(("dotty.runtime.function.JFunction" + arity))
+        else ctx.requiredClass(("scala.Function" + arity))
       }
     }
   }