VideoCommon: Move bounding box pixel quads rounding to shader

This avoids rounding values that the game writes to the bounding box
registers, especially the default values.

Source/Core/VideoCommon/RenderBase.cpp

@@ -187,18 +187,7 @@ void Renderer::ReinterpretPixelData(EFBReinterpretType convtype)
 
 u16 Renderer::BBoxRead(int index)
 {
-  u16 value = BBoxReadImpl(index);
-
-  // The GC/Wii GPU rasterizes in 2x2 pixel groups, so bounding box values will be rounded to the
-  // extents of these groups, rather than the exact pixel.
-  // This would have been handled in the pixel shader, but all attempts to do so did not work on
-  // OpenGL/NVIDIA, due to presumably mystical driver behavior with atomics.
-  if (index == 0 || index == 2)
-    value &= ~1;
-  else
-    value |= 1;
-
-  return value;
+  return BBoxReadImpl(index);
 }
 
 void Renderer::BBoxWrite(int index, u16 value)