RedundantLetInspection: fix false positive for inner lambda expression

#KT-25271 Fixed

idea/testData/inspectionsLocal/complexRedundantLet/withInnerFunction.kt

@@ -0,0 +1,11 @@
+// PROBLEM: none
+// WITH_RUNTIME
+
+
+val a = randomValue().let<caret> { r ->
+    List(10, fun(it: Int): Int {
+        return r
+    })
+}
+
+fun randomValue(): Int = 42

idea/testData/inspectionsLocal/complexRedundantLet/withInnerLambda.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+// WITH_RUNTIME
+
+
+val a = randomValue().let<caret> { r -> List(10) { r } }
+
+fun randomValue(): Int = 42