nep_invoker_blob can be simplified more

In FFM, native function would be called via `nep_invoker_blob`. If the function has two arguments, it would be following:

```
Decoding RuntimeStub - nep_invoker_blob 0x00007fcae394cd10
--------------------------------------------------------------------------------
  0x00007fcae394cd80: pushq %rbp
  0x00007fcae394cd81: movq %rsp, %rbp
  0x00007fcae394cd84: subq $0, %rsp
 ;; { argument shuffle
  0x00007fcae394cd88: movq %r8, %rax
  0x00007fcae394cd8b: movq %rsi, %r10
  0x00007fcae394cd8e: movq %rcx, %rsi
  0x00007fcae394cd91: movq %rdx, %rdi
 ;; } argument shuffle
  0x00007fcae394cd94: callq *%r10
  0x00007fcae394cd97: leave
  0x00007fcae394cd98: retq
```

`subq $0, %rsp` is for shadow space on stack, and `movq %r8, %rax` is number of args for variadic function. So they are not necessary in some case. They should be remove following if they are not needed:

```
Decoding RuntimeStub - nep_invoker_blob 0x00007fd8778e2810
--------------------------------------------------------------------------------
  0x00007fd8778e2880: pushq %rbp
  0x00007fd8778e2881: movq %rsp, %rbp
 ;; { argument shuffle
  0x00007fd8778e2884: movq %rsi, %r10
  0x00007fd8778e2887: movq %rcx, %rsi
  0x00007fd8778e288a: movq %rdx, %rdi
 ;; } argument shuffle
  0x00007fd8778e288d: callq *%r10
  0x00007fd8778e2890: leave
  0x00007fd8778e2891: retq
```

We can see these stub code on [ffmasm testcase](https://github.com/YaSuenag/ffmasm/tree/ef7a466ca9607164dbe7be7e68ea509d4bdac998/examples/cpumodel) with `-XX:+UnlockDiagnosticVMOptions -XX:+PrintStubCode` and hsdis library. This testcase linked the code with `Linker.Option.isTrivial()`.