Remove warning for running the compiler under Java 6/7

Now the compiler won't even start, so no need to check this manually.

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

@@ -79,9 +79,6 @@ public abstract class CommonCompilerArguments implements Serializable {
     @Argument(value = "Xno-check-impl", description = "Do not check presence of 'impl' modifier in multi-platform projects")
     public boolean noCheckImpl;
 
-    @Argument(value = "Xskip-java-check", description = "Do not warn when running the compiler under Java 6 or 7")
-    public boolean noJavaVersionWarning;
-
     @Argument(value = "Xcoroutines=warn")
     public boolean coroutinesWarn;