[IR] Remove IrFactory property from IrBlockBody and IrExpressionBody

in effort to simplify implementation classes when possible.

Those two properties always point to IrFactoryImpl, so it may as well
be used directly.

#KT-65773 In Progress

compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/IrTree.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2024 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -704,7 +704,6 @@ object IrTree : AbstractTreeBuilder() {
 
         parent(body)
 
-        +factory
         +field("expression", expression) {
             useFieldInIrFactory()
         }
@@ -715,8 +714,6 @@ object IrTree : AbstractTreeBuilder() {
 
         parent(body)
         parent(statementContainer)
-
-        +factory
     }
     val declarationReference: Element by element(Expression) {
         parent(expression)