[FIR-TEST] Update testdata of old frontend tests

compiler/testData/diagnostics/testsWithStdLib/tryCatch/correctSmartcasts.fir.kt

@@ -30,7 +30,7 @@ fun test2(s: String?) {
             requireNotNull(s)
             t2 = true
         }
-        t2.<!UNRESOLVED_REFERENCE!>not<!>()
+        t2.not()
         s.length
     }
 }

compiler/testData/diagnostics/testsWithStdLib/tryCatch/correctSmartcasts_after.fir.kt

@@ -31,7 +31,7 @@ fun test2(s: String?) {
             requireNotNull(s)
             t2 = true
         }
-        t2.<!UNRESOLVED_REFERENCE!>not<!>()
+        t2.not()
         s.length
     }
 }