KT-58862: Remove cinterop -mode option

metadata cinterop libraries perform pretty well for years,
so we can drop this flag.

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/jvm/CommandLine.kt

@@ -53,8 +53,6 @@ open class CommonInteropArguments(val argParser: ArgParser) {
             .default("unspecified")
     val repo by argParser.option(ArgType.String, shortName = "r", description = "repository to resolve dependencies")
             .multiple()
-    val mode by argParser.option(ArgType.Choice<GenerationMode>(), description = "the way interop library is generated")
-            .default(DEFAULT_MODE)
     val nodefaultlibs by argParser.option(ArgType.Boolean, NODEFAULTLIBS,
             description = "don't link the libraries from dist/klib automatically").default(false)
     val nodefaultlibsDeprecated by argParser.option(ArgType.Boolean, NODEFAULTLIBS_DEPRECATED,
@@ -76,10 +74,6 @@ open class CommonInteropArguments(val argParser: ArgParser) {
             fullName = "Xoverride-konan-properties",
             description = "Override konan.properties.values"
         ).multiple().delimiter(";")
-
-    companion object {
-        val DEFAULT_MODE = GenerationMode.METADATA
-    }
 }
 
 open class CInteropArguments(argParser: ArgParser =

kotlin-native/Interop/StubGenerator/src/main/kotlin/org/jetbrains/kotlin/native/interop/gen/jvm/main.kt

@@ -291,17 +291,6 @@ private fun processCLib(
 
     val outKtPkg = fqParts.joinToString(".")
 
-    val mode = run {
-        val providedMode = cinteropArguments.mode
-
-        if (providedMode == GenerationMode.METADATA && flavor == KotlinPlatform.JVM) {
-            warn("Metadata mode isn't supported for Kotlin/JVM! Falling back to sourcecode.")
-            GenerationMode.SOURCE_CODE
-        } else {
-            providedMode
-        }
-    }
-
     val resolver = getLibraryResolver(cinteropArguments, tool.target)
 
     val allLibraryDependencies = when (flavor) {
@@ -349,7 +338,10 @@ private fun processCLib(
     } else {
         {}
     }
-
+    val mode = when (flavor) {
+        KotlinPlatform.JVM -> GenerationMode.SOURCE_CODE
+        KotlinPlatform.NATIVE -> GenerationMode.METADATA
+    }
     val stubIrContext = StubIrContext(logger, configuration, nativeIndex, imports, flavor, mode, libName, plugin)
     val stubIrOutput = run {
         val outKtFileCreator = {