server: sync: make skip reason message more genenric

By specifying that the snapshot is being skipped because of the
condition met on the sync target instead of 'local', the same message
can be reused for the sync job in push direction without loosing
sense.

src/server/sync.rs

@@ -480,7 +480,8 @@ impl std::fmt::Display for SkipReason {
             f,
             "{}",
             match self {
-                SkipReason::AlreadySynced => "older than the newest local snapshot",
+                SkipReason::AlreadySynced =>
+                    "older than the newest snapshot present on sync target",
                 SkipReason::TransferLast => "due to transfer-last",
             }
         )