Stop the master relaying USER_SYNC for other workers (#7318)

Long story short: if we're handling presence on the current worker, we shouldn't be sending USER_SYNC commands over replication.

In an attempt to figure out what is going on here, I ended up refactoring some bits of the presencehandler code, so the first 4 commits here are non-functional refactors to move this code slightly closer to sanity. (There's still plenty to do here :/). Suggest reviewing individual commits.

Fixes (I hope) #7257.

1 files changed, 1 insertions, 5 deletions

diff --git a/docs/tcp_replication.md b/docs/tcp_replication.md

index 3be8e50c4c..b922d9cf7e 100644
--- a/docs/tcp_replication.md
+++ b/docs/tcp_replication.md
@@ -196,7 +196,7 @@ Asks the server for the current position of all streams.
 
 #### USER_SYNC (C)
 
-   A user has started or stopped syncing
+   A user has started or stopped syncing on this process.
 
 #### CLEAR_USER_SYNC (C)
 
@@ -216,10 +216,6 @@ Asks the server for the current position of all streams.
 
    Inform the server a cache should be invalidated
 
-#### SYNC (S, C)
-
-   Used exclusively in tests
-
 ### REMOTE_SERVER_UP (S, C)
 
    Inform other processes that a remote server may have come back online.