Don't output fi= and cfi= lines

The `fi=` and `cfi=` lines are making the call graph much less easy to follow.

```python
# source for /tmp/foo.py
import time

def func2():
    time.sleep(0.5)

def func1():
    time.sleep(0.5)
    for i in range(2):
        func2()

def main():
    time.sleep(0.5)
    func1()
    for i in range(3):
        func2()

main()
```

Running the profile:

```
python -m cProfile -o /tmp/foo.profile /tmp/foo.py
pyprof2calltree -i /tmp/foo.profile /tmp/foo.log
qcachegrind /tmp/foo.log
```

qcachegrind before this change (notice the duplicate entries and lack of complete graph):

![image](https://f.cloud.github.com/assets/150329/1570129/7905a5d6-50e3-11e3-9e4c-2e8c35b8d78e.png)

qcachegrind after this change:

![image](https://f.cloud.github.com/assets/150329/1570121/5713f02c-50e3-11e3-9d7d-bf20d9c58523.png)