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

compiler/testData/cli/jvm/extraHelp.out

@@ -12,7 +12,6 @@ where advanced options include:
   -Xadd-compiler-builtins    Add definitions of built-in declarations to the compilation classpath (useful with -no-stdlib)
   -Xload-builtins-from-dependencies
                              Load definitions of built-in declarations from module dependencies, instead of from the compiler
-  -Xinterface-compatibility  Generate DefaultImpls classes for interfaces in JVM target bytecode version 1.8 for binary compatibility with 1.6
   -Xno-inline                Disable method inlining
   -Xrepeat <count>           Repeat compilation (for performance analysis)
   -Xplugin <path>            Load plugins from the given classpath

compiler/testData/cli/jvm/jvm8Target.args

@@ -0,0 +1,6 @@
+$TESTDATA_DIR$/jvm8Target.kt
+-d
+$TEMP_DIR$
+-jvm-target
+1.8
+

compiler/testData/cli/jvm/jvm8Target.kt

@@ -0,0 +1,7 @@
+interface A {
+    fun test() = "OK"
+}
+
+fun main(args: Array<String>) {
+    println(object : A {}.test())
+}

compiler/testData/cli/jvm/jvm8Target.out

@@ -0,0 +1,2 @@
+warning: the -jvm-target option has no effect yet
+OK