Simplify diagnostic message for ACTUAL_MISSING

#KT-21939 Fixed

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -261,7 +261,7 @@ public class DefaultErrorMessages {
 
         MAP.put(NO_ACTUAL_CLASS_MEMBER_FOR_EXPECTED_CLASS, "Actual class ''{0}'' has no corresponding members for expected class members:{1}",
                 NAME, IncompatibleExpectedActualClassScopesRenderer.TEXT);
-        MAP.put(ACTUAL_MISSING, "Declaration should be marked with 'actual' (suppress with -Xno-check-actual)");
+        MAP.put(ACTUAL_MISSING, "Declaration must be marked with 'actual'");
 
         MAP.put(PROJECTION_ON_NON_CLASS_TYPE_ARGUMENT, "Projections are not allowed on type arguments of functions and properties");
         MAP.put(SUPERTYPE_NOT_INITIALIZED, "This type has a constructor, and thus must be initialized here");

compiler/testData/multiplatform/simpleNoImplKeywordOnTopLevelFunction/output.txt

@@ -5,6 +5,6 @@ Output:
 -- JVM --
 Exit code: COMPILATION_ERROR
 Output:
-compiler/testData/multiplatform/simpleNoImplKeywordOnTopLevelFunction/jvm.kt:3:5: error: declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+compiler/testData/multiplatform/simpleNoImplKeywordOnTopLevelFunction/jvm.kt:3:5: error: declaration must be marked with 'actual'
 fun foo(s: String): Array<CharSequence?> = arrayOf(s)
     ^

idea/testData/multiModuleQuickFix/addActualToClass/jvm/jvm.kt

@@ -1,4 +1,4 @@
 // "Add 'actual' modifier" "true"
-// ERROR: Declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+// ERROR: Declaration must be marked with 'actual'
 
 class <caret>Foo

idea/testData/multiModuleQuickFix/addActualToClass/jvm/jvm.kt.after

@@ -1,4 +1,4 @@
 // "Add 'actual' modifier" "true"
-// ERROR: Declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+// ERROR: Declaration must be marked with 'actual'
 
 actual class Foo

idea/testData/multiModuleQuickFix/addActualToClassMember/jvm/jvm.kt

@@ -1,5 +1,5 @@
 // "Add 'actual' modifier" "true"
-// ERROR: Declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+// ERROR: Declaration must be marked with 'actual'
 
 actual class Foo {
     fun <caret>foo() {}

idea/testData/multiModuleQuickFix/addActualToClassMember/jvm/jvm.kt.after

@@ -1,5 +1,5 @@
 // "Add 'actual' modifier" "true"
-// ERROR: Declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+// ERROR: Declaration must be marked with 'actual'
 
 actual class Foo {
     actual fun foo() {}

idea/testData/multiModuleQuickFix/addActualToTopLevelMember/jvm/jvm.kt

@@ -1,4 +1,4 @@
 // "Add 'actual' modifier" "true"
-// ERROR: Declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+// ERROR: Declaration must be marked with 'actual'
 
 fun <caret>foo() {}

idea/testData/multiModuleQuickFix/addActualToTopLevelMember/jvm/jvm.kt.after

@@ -1,4 +1,4 @@
 // "Add 'actual' modifier" "true"
-// ERROR: Declaration should be marked with 'actual' (suppress with -Xno-check-actual)
+// ERROR: Declaration must be marked with 'actual'
 
 actual fun foo() {}