[FIR2IR] Remove special handling of named arguments for vararg

FirNamedArgumentExpressions don't exist anymore during FIR2IR phase
and so handling FirSpreadArgumentExpression in Fir2IrVisitor is
sufficient.

#KT-66124

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -550,7 +550,7 @@ class Fir2IrVisitor(
     }
 
     private fun FirExpression.convertToIrVarargElement(): IrVarargElement =
-        if (this is FirSpreadArgumentExpression || this is FirNamedArgumentExpression && this.isSpread) {
+        if (this is FirSpreadArgumentExpression) {
             IrSpreadElementImpl(
                 source?.startOffset ?: UNDEFINED_OFFSET,
                 source?.endOffset ?: UNDEFINED_OFFSET,

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/CallAndReferenceGenerator.kt

@@ -1072,27 +1072,9 @@ class CallAndReferenceGenerator(
             }
         }
         return irArgument
-            .applyAssigningArrayElementsToVarargInNamedForm(unwrappedArgument, parameter)
             .applyImplicitIntegerCoercionIfNeeded(unwrappedArgument, parameter)
     }
 
-    private fun IrExpression.applyAssigningArrayElementsToVarargInNamedForm(
-        argument: FirExpression,
-        parameter: FirValueParameter?,
-    ): IrExpression {
-        if (this is IrVararg && parameter?.isVararg == true && argument is FirVarargArgumentsExpression && elements.size == 1) {
-            val irVarargElement = elements[0]
-            if (argument.arguments[0] is FirNamedArgumentExpression &&
-                // IrVarargElement can be either IrSpreadElement (then nothing to do) or IrExpression
-                irVarargElement is IrExpression &&
-                (irVarargElement.type.isArray() || irVarargElement.type.isPrimitiveArray() || irVarargElement.type.isUnsignedArray())
-            ) {
-                elements[0] = IrSpreadElementImpl(irVarargElement.startOffset, irVarargElement.endOffset, irVarargElement)
-            }
-        }
-        return this
-    }
-
     private fun IrExpression.applyImplicitIntegerCoercionIfNeeded(
         argument: FirExpression,
         parameter: FirValueParameter?,