[LL FIR] avoid redundant pass through the entire super type hierarchy for nested classes

We can omit this step in LL FIR because, according to the contract,
an outer class must be resolved before nested class
Also, it drops unsafe access to superTypeRefs from FIR transformer

^KT-56550

analysis/low-level-api-fir/testdata/lazyResolve/classes/nestedClass.kt

@@ -0,0 +1,5 @@
+open class TopLevelClass
+open class AnotherTopLevelClass : TopLevelClass()
+class OuterClass : AnotherTopLevelClass() {
+    class Nested<caret>Class
+}