Remove disable catchup through snapshot transfer functionality (we never used this in 4 years)

Summary: as tilte

Reviewed By: SarahDesouky

Differential Revision: D82555691

fbshipit-source-id: beffc0ab409b98286f7c75f8390deaaab95ea973

Author: Jose-Angel Herrero Bajo

include/wa_raft.hrl

@@ -257,9 +257,6 @@
     (?RAFT_APP_CONFIG(App, ?RAFT_LOG_HEARTBEAT_BINARY_ENTRIES, false) =:= true)
 ).
 
-%% Whether or not the RAFT server should use any special catchup strategy to bring peers back in sync.
--define(RAFT_CATCHUP_ENABLED, raft_catchup_enabled).
--define(RAFT_CATCHUP_ENABLED(App), (?RAFT_APP_CONFIG(App, {?RAFT_CATCHUP_ENABLED, catchup_enabled}, true) =/= false)).
 %% Minimum number of log entries after which RAFT servers should use bulk logs catchup to bring peers
 %% back into sync if enabled.
 -define(RAFT_CATCHUP_THRESHOLD, raft_catchup_threshold).

src/wa_raft_server.erl

@@ -3473,12 +3473,9 @@ select_follower_replication_mode(
         last_applied = LastAppliedIndex
     }
 ) ->
-    CatchupEnabled = ?RAFT_CATCHUP_ENABLED(App),
     BulkLogThreshold = ?RAFT_CATCHUP_THRESHOLD(App),
     LeaderFirstIndex = wa_raft_log:first_index(View),
     if
-        % If catchup modes are not enabled, then always replicate using logs.
-        not CatchupEnabled                                      -> logs;
         % Snapshot is required if the follower is stalled or we are missing
         % the logs required for incremental replication.
         FollowerLastIndex =:= 0                                 -> snapshot;