Remove outdated thread default auto archive time

Fixes discord#5873

Author: ajpalkovic

docs/topics/Threads.md

@@ -54,7 +54,7 @@ Because of this constraint, the gateway protocol is designed to ensure that bots
 
 Threads do not count against the max-channels limit in a guild, but there is a limit on the maximum number of active threads in a guild.
 
-Threads automatically archive after 7 days of inactivity (as a server approaches the max thread limit this timer will automatically lower, but never below the `auto_archive_duration`). "Activity" is defined as sending a message, unarchiving a thread, or changing the auto-archive time. The `auto_archive_duration` field previously controlled how long a thread could stay active, but is now repurposed to control how long the thread stays in the channel list. Channels can also set `default_auto_archive_duration`, which is used by our clients to pre-select a different `auto_archive_duration` value when a user creates a thread.
+Threads automatically archive after a period of inactivity (as a server approaches the max thread limit this timer will automatically lower, but never below the `auto_archive_duration`). "Activity" is defined as sending a message, unarchiving a thread, or changing the auto-archive time. The `auto_archive_duration` field previously controlled how long a thread could stay active, but is now repurposed to control how long the thread stays in the channel list. Channels can also set `default_auto_archive_duration`, which is used by our clients to pre-select a different `auto_archive_duration` value when a user creates a thread.
 
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