Move RunForMillis.cpp to the .cpp file.

Remove RunMillis and RunForCycles. I know this gets rid of parallelism in naming, but the alternate versions read wrong to me

testing/SimHarness.cpp

@@ -30,6 +30,13 @@ void SimHarness::RunCycles(size_t n) {
   for (size_t i = 0; i < n; ++i) RunCycle();
 }
 
+void SimHarness::RunForMillis(size_t t) {
+  auto start_time = Kaleidoscope.millisAtCycleStart();
+  while (Kaleidoscope.millisAtCycleStart() - start_time < t) {
+    RunCycle();
+  }
+}
+
 void SimHarness::Press(KeyAddr key_addr) {
   Kaleidoscope.device().keyScanner().setKeystate(
     key_addr,

testing/SimHarness.h

@@ -29,17 +29,7 @@ class SimHarness {
  public:
   void RunCycle();
   void RunCycles(size_t n);
-  void RunForCycles(size_t n) {
-    RunCycles(n);
-  }
-
-  void RunMillis(size_t t) {
-    RunCycles(t);
-  }
-  void RunForMillis(size_t t) {
-    RunMillis(t);
-  }
-
+  void RunForMillis(size_t t);
   void Press(KeyAddr key_addr);
   void Release(KeyAddr key_addr);
   void Press(uint8_t row, uint8_t col);