[NI] Remove hack for special functions

Treating special functions for `if`, `when`, `try`, `?:` as not accepting `Nothing` result type is incorrect.
Making so leads to cases with uninferred `Nothing` result type for inner calls and lost data flow info.

compiler/testData/diagnostics/tests/regressions/testNestedSpecialCalls.fir.kt

@@ -0,0 +1,11 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNREACHABLE_CODE
+
+fun test() {
+    val x: Int? = 20
+    if (x != null) {
+    } else {
+        if (true) return else return
+    }
+    x.and(1) // unsafe call
+}