[PLUGIN API] Drop PureIrGenerationExtension

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/extensions/IrGenerationExtension.kt

@@ -5,7 +5,6 @@
 
 package org.jetbrains.kotlin.backend.common.extensions
 
-import org.jetbrains.kotlin.backend.common.CommonBackendContext
 import org.jetbrains.kotlin.extensions.ProjectExtensionDescriptor
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 
@@ -17,15 +16,3 @@ interface IrGenerationExtension {
 
     fun generate(moduleFragment: IrModuleFragment, pluginContext: IrPluginContext)
 }
-
-// Extension point for plugins which run before any lowerings, but after the Ir has been constructed.
-@Deprecated("This is a temporary class which will be replaced with another extension mechanism soon.", level = DeprecationLevel.ERROR)
-interface PureIrGenerationExtension {
-    @Suppress("DEPRECATION_ERROR")
-    companion object :
-        ProjectExtensionDescriptor<PureIrGenerationExtension>(
-            "org.jetbrains.kotlin.pureIrGenerationExtension", PureIrGenerationExtension::class.java
-        )
-
-    fun generate(moduleFragment: IrModuleFragment, context: CommonBackendContext)
-}