remove support for 'trait' keyword

Original commit: 4ca434da54

jps/jps-plugin/testData/general/DependencyToOldKotlinLib/module/src/module/A.kt

@@ -1,6 +1,6 @@
 package module
 
-public trait A {
+public interface  A {
     fun oldFun(): Int = 1
     fun newFun(): Int = 42
 }