[IR] Remove unused Ir.irModule property

It is required for the Native backend refactoring
where `Context` does not contain a reference for any
particular IrModuleFragment.

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt

@@ -123,7 +123,7 @@ class WasmBackendContext(
     override val propertyLazyInitialization: PropertyLazyInitialization =
         PropertyLazyInitialization(enabled = propertyLazyInitialization, eagerInitialization = wasmSymbols.eagerInitialization)
 
-    override val ir = object : Ir<WasmBackendContext>(this, irModuleFragment) {
+    override val ir = object : Ir<WasmBackendContext>(this) {
         override val symbols: Symbols = wasmSymbols
         override fun shouldGenerateHandlerParameterForDefaultBodyFun() = true
     }