Switch to auto generated IR tree

Co-authored-by: Alexander Udalov <alexander.udalov@jetbrains.com>

compiler/ir/ir.tree/tree-generator/ReadMe.md

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+# IR tree generator
+
+This module generates the IR tree interfaces and classes, as well as visitors and transformers.
+
+The generator is run on every build. If you change something in the model or in the generator code, just run `./gradlew dist` and the generator task will run before the start of the compilation.
+
+The model is declared in [IrTree.kt](src/org/jetbrains/kotlin/ir/generator/IrTree.kt).
+
+You can navigate to the model from a generated `Ir*` class by following the `@sample` link in its kdoc.