fix -Wpessimizing-move warnings
fix -Wpessimizing-move warnings

```
/vagrant/src/main.cpp:861:16: warning: moving a temporary object prevents copy elision [-Wpessimizing-move]
    bytecode = std::move(bpforc->getBytecode());
               ^
/vagrant/src/main.cpp:861:16: note: remove std::move call here
    bytecode = std::move(bpforc->getBytecode());
               ^~~~~~~~~~
```

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace