Drop obsolete annotations syntax

compiler/testData/psi/examples/array/MutableArray.kt

@@ -3,11 +3,11 @@
 */
 
 open class ReadOnlyArray<out T> : ISized {
-  [operator] fun get(index : Int) : T
+  @[operator] fun get(index : Int) : T
 }
 
 open class WriteOnlyArray<in T> : ISized { // This is needed to keep IIterator's <T> covariant
-  [operator] fun set(index : Int, value : T)
+  @[operator] fun set(index : Int, value : T)
 }
 
 class MutableArray<T> : ReadOnlyArray<T>, WriteOnlyArray<T> {/*...*/}