Minor: cleanup + support variance in ErrorListDiagnosticListRenderer

1. Support variance in ErrorListDiagnosticListRenderer.
   I will make some diagnostics to have covariant type arguments in the
   next commits
2. Drop unused code

Review: https://jetbrains.team/p/kt/reviews/12750/timeline

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/model/ErrorListDiagnosticListRenderer.kt

@@ -13,6 +13,7 @@ import java.io.File
 import kotlin.reflect.KClass
 import kotlin.reflect.KType
 import kotlin.reflect.KTypeProjection
+import kotlin.reflect.KVariance
 
 object ErrorListDiagnosticListRenderer : DiagnosticListRenderer() {
     const val BASE_PACKAGE = "org.jetbrains.kotlin.fir.analysis.diagnostics"
@@ -116,6 +117,11 @@ object ErrorListDiagnosticListRenderer : DiagnosticListRenderer() {
         if (typeArgumentType == null) {
             print("*")
         } else {
+            when (typeArgument.variance) {
+                KVariance.INVARIANT, null -> {}
+                KVariance.IN -> print("in ")
+                KVariance.OUT -> print("out ")
+            }
             printType(typeArgumentType)
         }
     }

core/compiler.common/src/org/jetbrains/kotlin/resolve/multiplatform/ExpectActualCompatibility.kt

@@ -105,11 +105,3 @@ val ExpectActualCompatibility<*>.isCompatibleOrWeaklyIncompatible: Boolean
 
 val ExpectActualCompatibility<*>.compatible: Boolean
     get() = this == ExpectActualCompatibility.Compatible
-
-@OptIn(ExperimentalContracts::class)
-fun ExpectActualCompatibility<*>.isIncompatible(): Boolean {
-    contract {
-        returns(true) implies (this@isIncompatible is ExpectActualCompatibility.Incompatible<*>)
-    }
-    return !compatible
-}