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/plusplusMinusminus.kt

@@ -1,4 +1,3 @@
-// !WITH_NEW_INFERENCE
 fun foo(arg: Int?): Int {
     var i = arg
     if (i != null && <!DEBUG_INFO_SMARTCAST!>i<!>++ == 5) {