[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.

js/js.tests/test/org/jetbrains/kotlin/benchmarks/GenerateIrRuntime.kt

@@ -601,7 +601,6 @@ class GenerateIrRuntime {
             module.descriptor,
             irBuiltIns,
             symbolTable,
-            module,
             additionalExportedDeclarationNames = emptySet(),
             keep = emptySet(),
             configuration