Infinite growing dictionary in Dispersy statistics

[devos50]

The dictionaries stored in the Dispersy statistics (MessageStatistics) are always growing and never pruned. When running Tribler for extended periods of time, this leads to significant memory usage. See for instance https://github.com/Tribler/dispersy/blob/devel/statistics.py#L82. It seems that we're storing full details about all introduction requests sent and received. The same goes for walk_failure_dict.

To fix this, we can either periodically prune the dictionaries or disable the Dispersy statistics. @qstokkink do you have any comments on this? I think it's important enough to fix this for Tribler 7.1 👍

[qstokkink]

Dispersy is end of life, ~~therefore I will close this issue.~~ so we can simply remove/disable these statistics imo.

[devos50]

Great!