Use Yamux configuration in Praefect by default

praefect_use_yamux_configuration_for_gitaly feature flag enables Praefect to read Yamux configuration from the config file. This commit removes the feature flag and enables the new default settings that were tested behind it. We're skipping default enabling the flag as it requires two connections sets and the feature flagged connections are not used for all of the functionality like elections. To avoid this complexity, we'll just remove the flag directly and enable the new defaults. The new defaults lower the receive buffer size in Yamux leading to less memory usage but possibly worse throughput in high latency scenarios. We were previously using custom settings but are now returning to the Yamux defaults as they are also used in the clients for the sidechannels. This ensures Praefect doesn't buffer excessively with sidechannels in use.

Related to #4644 (closed)