fix self-coded remap function

[xmba15]

current self-coded remap function only uses bilinear remapping method and the result corner looks crooked as can be seen in here.

opencv's builtin function provides better result.

-> need to fix the current mapping.

[xmba15]

will do when have time.

[xmba15]

https://github.com/xmba15/camera_instrinsic_calibration/blob/master/src/Undistortion.cpp#L204