remove support for 'trait' keyword

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
 }

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

@@ -1,5 +1,5 @@
 package module
 
-public trait A {
+public interface A {
     fun oldFun(): Int = 1
 }

jps-plugin/testData/incremental/pureKotlin/traitClassObjectConstantChanged/const.kt

@@ -1,6 +1,6 @@
 package test
 
-trait Trait {
+interface Trait {
     companion object {
         // Old and new constant values are different, but their hashes are the same
         val CONST = "BF"

jps-plugin/testData/incremental/pureKotlin/traitClassObjectConstantChanged/const.kt.new

@@ -1,6 +1,6 @@
 package test
 
-trait Trait {
+interface Trait {
     companion object {
         // Old and new constant values are different, but their hashes are the same
         val CONST = "Ae"