Remove 'Minimum Thinking Time' UCI option.

the option was, since at least 2014, not correctly implemented,
ignoring all dynamic adjustments to optimum time in search.
Instead of fixing it, remove it, no need to expose an option that
will influence time management negatively.

closes https://github.com/official-stockfish/Stockfish/pull/2765

No functional change.

src/ucioption.cpp

@@ -68,7 +68,6 @@ void init(OptionsMap& o) {
   o["MultiPV"]               << Option(1, 1, 500);
   o["Skill Level"]           << Option(20, 0, 20);
   o["Move Overhead"]         << Option(10, 0, 5000);
-  o["Minimum Thinking Time"] << Option( 0, 0, 5000);
   o["Slow Mover"]            << Option(100, 10, 1000);
   o["nodestime"]             << Option(0, 0, 10000);
   o["UCI_Chess960"]          << Option(false);