Shorten the audit log reason appropriately, remove unused vars (#4189)

* [Mod] Check for reason length & remove unused vars

This PR also remove unused variable.

* Blame me

* Apply Kowlin order.

Text will get truncate in audit logs in case we're going over 512 characters.

* This is already handled by ban_user()

* Use `get_audit_reason()` in `[p]tempban`

* Add a new kwarg to `get_audit_reason()` instead

* Include `[p]voiceban` and `[p]voiceunban`

* Include Mutes cog

Co-authored-by: jack1142 <6032823+jack1142@users.noreply.github.com>

redbot/core/utils/mod.py

@@ -67,7 +67,7 @@ async def slow_deletion(messages: Iterable[discord.Message]):
             pass
 
 
-def get_audit_reason(author: discord.Member, reason: str = None):
+def get_audit_reason(author: discord.Member, reason: str = None, *, shorten: bool = False):
     """Construct a reason to appear in the audit log.
 
     Parameters
@@ -76,6 +76,9 @@ def get_audit_reason(author: discord.Member, reason: str = None):
         The author behind the audit log action.
     reason : str
         The reason behind the audit log action.
+    shorten : bool
+        When set to ``True``, the returned audit reason string will be
+        shortened to fit the max length allowed by Discord audit logs.
 
     Returns
     -------
@@ -83,11 +86,14 @@ def get_audit_reason(author: discord.Member, reason: str = None):
         The formatted audit log reason.
 
     """
-    return (
+    audit_reason = (
         "Action requested by {} (ID {}). Reason: {}".format(author, author.id, reason)
         if reason
         else "Action requested by {} (ID {}).".format(author, author.id)
     )
+    if shorten and len(audit_reason) > 512:
+        audit_reason = f"{audit_reason[:509]}..."
+    return audit_reason
 
 
 async def is_allowed_by_hierarchy(