FIC: remove isFun from IR proto as conversion should happen in psi2ir

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt

@@ -294,8 +294,7 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
                 isData = false,
                 isExternal = false,
                 isInline = false,
-                isExpect = false,
-                isFun = false
+                isExpect = false
             ).apply {
                 d.bind(this)
                 parent = irFunction.parent

compiler/ir/backend.common/src/org/jetbrains/kotlin/ir/builders/declarations/declarationBuilders.kt

@@ -27,7 +27,7 @@ fun IrClassBuilder.buildClass(): IrClass {
         IrClassSymbolImpl(wrappedDescriptor),
         name, kind, visibility, modality,
         isCompanion = isCompanion, isInner = isInner, isData = isData, isExternal = isExternal,
-        isInline = isInline, isExpect = isExpect, isFun = isFun
+        isInline = isInline, isExpect = isExpect
     ).also {
         wrappedDescriptor.bind(it)
     }