Make effort part of RootMove struct

Also includes several small cleanups.

Passed STC:
https://tests.stockfishchess.org/tests/view/65f15cfe0ec64f0526c473a0
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 71136 W: 18456 L: 18273 D: 34407
Ptnml(0-2): 311, 8014, 18708, 8251, 284

closes https://github.com/official-stockfish/Stockfish/pull/5114

No functional change

src/thread.cpp

@@ -19,7 +19,6 @@
 #include "thread.h"
 
 #include <algorithm>
-#include <array>
 #include <cassert>
 #include <deque>
 #include <memory>
@@ -211,7 +210,6 @@ void ThreadPool::start_thinking(const OptionsMap&  options,
         th->worker->rootPos.set(pos.fen(), pos.is_chess960(), &th->worker->rootState);
         th->worker->rootState = setupStates->back();
         th->worker->tbConfig  = tbConfig;
-        th->worker->effort    = {};
     }
 
     main_thread()->start_searching();