Always use default 1.6 build target unless of 'jvm-target' option

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.java

@@ -111,9 +111,6 @@ public class K2JVMCompilerArguments extends CommonCompilerArguments {
     @Argument(value = "Xload-builtins-from-dependencies", description = "Load definitions of built-in declarations from module dependencies, instead of from the compiler")
     public boolean loadBuiltInsFromDependencies;
 
-    @Argument(value = "Xinterface-compatibility", description = "Generate DefaultImpls classes for interfaces in JVM target bytecode version 1.8 for binary compatibility with 1.6")
-    public boolean interfaceCompatibility;
-
     // Paths to output directories for friend modules.
     public String[] friendPaths;