Revert "Cycles: Use half storage for 16bit files (e.g. 16bit pngs) as well."

After discussion in IRC, 16bit int should not be converted to half, too much precision loss.

intern/cycles/render/image.cpp

@@ -176,9 +176,7 @@ ImageManager::ImageDataType ImageManager::get_image_metadata(const string& filen
 			}
 
 			/* check if it's half float */
-			if(spec.format == TypeDesc::HALF ||
-			   spec.format == TypeDesc::USHORT ||
-			   spec.format == TypeDesc::SHORT)
+			if(spec.format == TypeDesc::HALF)
 				is_half = true;
 
 			channels = spec.nchannels;