Delay UNUSED_PARAMETER on main parameter until 1.4 (part of KT-26999)

compiler/testData/diagnostics/tests/controlFlowAnalysis/mainWith12.kt

@@ -1,5 +0,0 @@
-// !LANGUAGE: -ExtendedMainConvention
-
-fun main(args: Array<String>) {
-
-}

compiler/testData/diagnostics/tests/controlFlowAnalysis/mainWithWarningOnUnusedParam.kt

@@ -1,3 +1,5 @@
+// !LANGUAGE: +WarningOnMainUnusedParameter
+
 fun main(<!UNUSED_PARAMETER!>args<!>: Array<String>) {
 
 }

compiler/testData/diagnostics/tests/controlFlowAnalysis/mainWithoutWarningOnUnusedParam.kt

@@ -0,0 +1,5 @@
+// !LANGUAGE: -WarningOnMainUnusedParameter
+
+fun main(args: Array<String>) {
+
+}