GDAL 3.13 introduced a --legacy switch in #14117 to fallback to the traditionnal code base of gdal2tiles, instead of the default mapping to "gdal raster tile", with a deprecation warning that it will be removed in GDAL 3.15.
So this task is about removing all the compatible code, and making gdal2tiles only a shim of gdal raster tile
GDAL 3.13 introduced a --legacy switch in #14117 to fallback to the traditionnal code base of gdal2tiles, instead of the default mapping to "gdal raster tile", with a deprecation warning that it will be removed in GDAL 3.15.
So this task is about removing all the compatible code, and making gdal2tiles only a shim of gdal raster tile