Possible bcc memory leak

Testing with `cat ./test.py ; python3 ./test.py & pid=$! ; sleep 1 ; grep VmRSS /proc/$pid/status ; sleep 60 ; grep VmRSS /proc/$pid/status ; kill $pid ;` we see this output:

```
import gc
from bcc import BPF
while True:
bpf = BPF(text="BPF_ARRAY(t);")
bpf.cleanup()
gc.collect()
VmRSS: 91828 kB
VmRSS: 93388 kB
```

1) It seems that there is some minor memory leak during bpf.cleanup(), this is irrelevant for simple scripts but for long-running daemons that dynamically attach/detach BPF programs this is more relevant.

2) Overall memory consumption is perhaps a bit high, for example on my laptop only gnome-shell and firefox are currently using more memory (RSS) than the most simple BCC example (`pidpersec`), processes like X, totem (playing audio), NetworkManager, etc are using less memory.

Thanks.

Start with the test.py loop using BPF(text="BPF_ARRAY(t);") and bpf.cleanup(), then reproduce the VmRSS measurements before and after the 60-second interval. Trace the cleanup path and compare it with the pidpersec example; done means identifying the source of the growth and adding a regression check for repeated attach/detach cycles.

Written by the indexing model from the issue text.