[Test] Fix FileNotFoundException in removeDirectiveFromFile

This happened when a FIR test didn't have a .fir.kt file.

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/utils/FileUtils.kt

@@ -27,6 +27,8 @@ fun File.isDirectiveDefined(directive: String): Boolean = this.useLines { line -
 }
 
 fun File.removeDirectiveFromFile(directive: Directive) {
+    if (!exists()) return
+
     val directiveName = directive.name
     val directiveRegexp = "^// $directiveName(:.*)?$(\n)?".toRegex(RegexOption.MULTILINE)
     val text = readText()
@@ -34,4 +36,4 @@ fun File.removeDirectiveFromFile(directive: Directive) {
         ?: error("Directive $directiveName was not found in $this")
     val textWithoutDirective = text.removeRange(directiveRange)
     writeText(textWithoutDirective)
-}
+}