Remove enable raft gating for block dump threads

Summary:
Partial revert of D28774820.

This gate seems to be added after a minor comment during review.
However, `block_dump_threads`, is set during the check phase for
`enable_raft_plugin`. By gating the blocking on `enable_raft_plugin`, we
pretty much make sure it'll never work.

`block_dump_threads` is only set in https://fburl.com/code/ksk6v3yc, and
that function is only called in Raft Listener + enable raft.

I think removing the gate should be free of side effects, but another
pair of eyes would be appreciated.

Reviewed By: abhinav04sharma

Differential Revision: D35200233

fbshipit-source-id: 779426173e8049df66013a55ed38c443d3227d8b

sql/rpl_binlog_sender.cc

@@ -240,7 +240,7 @@ void Binlog_sender::init() {
   thd->push_diagnostics_area(&m_diag_area);
   init_heartbeat_period();
   m_last_event_sent_ts = now_in_nanosecs();
-  if (enable_raft_plugin && block_dump_threads) {
+  if (block_dump_threads) {
     set_unknown_error("Binlog dump threads are blocked!");
     return;
   }