Make ExperimentFlags a singleton, remove inheritance relationships

src/app/emu/cpu/cpu.cc

@@ -1803,7 +1803,7 @@ void Cpu::ExecuteInstruction(uint8_t opcode) {
 
 void Cpu::LogInstructions(uint16_t PC, uint8_t opcode, uint16_t operand,
                           bool immediate, bool accumulator_mode) {
-  if (flags()->kLogInstructions) {
+  if (core::ExperimentFlags::get().kLogInstructions) {
     std::ostringstream oss;
     oss << "$" << std::uppercase << std::setw(2) << std::setfill('0')
         << static_cast<int>(PB) << ":" << std::hex << PC << ": 0x"

src/app/emu/cpu/cpu.h

@@ -34,7 +34,7 @@ class InstructionEntry {
   std::string instruction;  // Human-readable instruction text
 };
 
-class Cpu : public core::ExperimentFlags {
+class Cpu {
  public:
   explicit Cpu(Memory& mem, Clock& vclock, CpuCallbacks& callbacks)
       : memory(mem), clock(vclock), callbacks_(callbacks) {}