UPBGE: Fix first frame timing gap.

Previously when the engine started (StartEngine called) the
clock time and the frame time were set to the system real time.
But as the system (LA_System) was created before the conversion
of the blender data, at each run the engine started with a
different clock and frame time. This produce that render test
failed in most of case because animation were played with a
time gap due to the first frame.

To solve this issue the clock and frame time are let to 0 and
only m_previousRealTime is set in StartEngine. Indeed the
clock time is incremented in NextFrame based on m_previousRealTime
gap with current time and frame time is also incremented in the
same function.

source/gameengine/Ketsji/KX_KetsjiEngine.cpp

@@ -146,7 +146,6 @@ KX_KetsjiEngine::KX_KetsjiEngine(KX_ISystem *system)
 	m_flags(AUTO_ADD_DEBUG_PROPERTIES),
 	m_frameTime(0.0f),
 	m_clockTime(0.0f),
-	m_previousClockTime(0.0f),
 	m_previousAnimTime(0.0f),
 	m_timescale(1.0f),
 	m_previousRealTime(0.0f),
@@ -234,9 +233,6 @@ void KX_KetsjiEngine::SetConverter(KX_BlenderConverter *converter)
 
 void KX_KetsjiEngine::StartEngine()
 {
-	m_clockTime = m_kxsystem->GetTimeInSeconds();
-	m_frameTime = m_kxsystem->GetTimeInSeconds();
-	m_previousClockTime = m_kxsystem->GetTimeInSeconds();
 	m_previousRealTime = m_kxsystem->GetTimeInSeconds();
 
 	m_bInitialized = true;

source/gameengine/Ketsji/KX_KetsjiEngine.h

@@ -177,8 +177,6 @@ class KX_KetsjiEngine
 	double m_frameTime;
 	/// game time for the next rendering step
 	double m_clockTime;
-	/// game time of the previous rendering step
-	double m_previousClockTime;
 	///game time when the animations were last updated
 	double m_previousAnimTime;
 	double m_remainingTime;