- By not waiting `repl-diskless-sync-delay` when we don't have to, we
can reduce ~30% of dual channel tests execution time.
- This commit also drops one test which is not required for regular sync
(`Sync should continue if not all slaves dropped`).
- Skip dual channel test with master diskless disabled because it will
initiate the same synchronization process as the non-dual channel test,
making it redundant.
Before:
```
Execution time of different units:
171 seconds - integration/dual-channel-replication
305 seconds - integration/replication-psync
\o/ All tests passed without errors!
```
After:
```
Execution time of different units:
120 seconds - integration/dual-channel-replication
236 seconds - integration/replication-psync
\o/ All tests passed without errors!
```
Discused on https://github.com/valkey-io/valkey/pull/1173
---------
Signed-off-by: naglera <anagler123@gmail.com>