Use less reduction for escaping moves

This patch reuses the threatenedPieces variable (which is calculated in movepicker)
to reduce less in the search tree the moves which escape a capture.

passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 314352 W: 84042 L: 83328 D: 146982
Ptnml(0-2): 1105, 35084, 84207, 35552, 1228
https://tests.stockfishchess.org/tests/view/63355f37a004bed9a2e4a17f

passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 90752 W: 24556 L: 24147 D: 42049
Ptnml(0-2): 59, 8855, 27123, 9296, 43
https://tests.stockfishchess.org/tests/view/63383a7735f43d649ff5fa8b

closes https://github.com/official-stockfish/Stockfish/pull/4181

bench: 4114228

src/uci.cpp

@@ -224,7 +224,7 @@ namespace {
 
 /// UCI::loop() waits for a command from the stdin, parses it and then calls the appropriate
 /// function. It also intercepts an end-of-file (EOF) indication from the stdin to ensure a
-/// graceful exit if the GUI dies unexpectedly. When called with some command-line arguments, 
+/// graceful exit if the GUI dies unexpectedly. When called with some command-line arguments,
 /// like running 'bench', the function returns immediately after the command is executed.
 /// In addition to the UCI ones, some additional debug commands are also supported.
 
@@ -240,7 +240,7 @@ void UCI::loop(int argc, char* argv[]) {
       cmd += std::string(argv[i]) + " ";
 
   do {
-      if (argc == 1 && !getline(cin, cmd)) // Wait for an input or an end-of-file (EOF) indication 
+      if (argc == 1 && !getline(cin, cmd)) // Wait for an input or an end-of-file (EOF) indication
           cmd = "quit";
 
       istringstream is(cmd);