remove unused NativeInstruction::test methods

These methods were probably used during porting but were never called since. And only SPARC implements them.

$ ack "test\(" src/{,closed}/cpu/*/vm/nativeInst*.{cpp,hpp}
src/cpu/sparc/vm/nativeInst_sparc.cpp
177:void NativeCall::test() {
266:void NativeFarCall::test() {
356:void NativeMovConstReg::test() {
476:void NativeMovConstRegPatching::test() {
561:void NativeMovRegMem::test() {
706:void NativeMovRegMemPatching::test() {
836:void NativeJump::test() {

src/cpu/sparc/vm/nativeInst_sparc.hpp
269: static void test() {} // override for testing
315: static void test();
419: static void test();
488: static void test();
547: static void test();
644: static void test();
734: static void test();
806: static void test();

src/cpu/x86/vm/nativeInst_x86.hpp
96: static void test() {} // override for testing
213: static void test() {}
316: static void test() {}
366: static void test() {}
421: static void test() {}

src/closed/cpu/ppc/vm/nativeInst_ppc.cpp
225:void NativeMovConstReg::test() {
355:void NativeMovRegMem::test() {
550:void NativeJump::test() {

src/closed/cpu/arm/vm/nativeInst_arm.hpp
56: static void test() {}

src/closed/cpu/ppc/vm/nativeInst_ppc.hpp
237: static void test() {} // override for testing
300: static void test();
380: static void test();
430: static void test();
505: static void test();
565: static void test();