Bump version of Snowflake in Tor Browser to 221f1c41

In addition to some code refactors and cleanups, we've added some new features and fixes to the Snowflake client since the last version shipped in Tor Browser:

Moved client messages to the broker into the HTTP body
Fixed some race condition bugs
AMP cache rendezvous
Added the ability to specify Snowflake command-line arguments through SOCKS so they can be used as Bridge lines
Some performance tuning for KCP/smux

In particular, the AMP cache feature might be useful in near future blocking attempts of Snowflake.

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