Remove WITH_NEW_INFERENCE directive from all tests

This directive anyway does not make test run twice with OI, and with NI
It only once run the test with specific settings (// LANGUAGE)
and ignores irrelevant (OI or NI tags)

compiler/testData/diagnostics/tests/smartCasts/varnotnull/forEach.kt

@@ -1,4 +1,3 @@
-// !WITH_NEW_INFERENCE
 data class SomeObject(val n: SomeObject?) {
     fun doSomething() {}
     fun next(): SomeObject? = n