Revert "[NI] Fix reporting smartcast diagnostics for intersection types"

This reverts commit 033d7262

That commit breaks bootstraping

compiler/testData/diagnostics/tests/smartCasts/kt30826.kt

@@ -1,19 +0,0 @@
-// !WITH_NEW_INFERENCE
-// Issue: KT-30826
-
-interface I1
-interface I2 {
-    fun foo() {}
-}
-
-class A : I1, I2
-
-fun foo(x: I1?) {
-    var y = x
-    y as I2
-    val bar = {
-        <!SMARTCAST_IMPOSSIBLE!>y<!>.foo() // NPE in NI, smartcast impossible in OI
-    }
-    y = null
-    bar()
-}