Redundant level data fixer files are saved in worlds' "data" folder

Steps to Reproduce

• Create a new world in 24w45a.

• Enter this world.

• Exit this world.

• View files under level file <level name>/data/.

Expected Result

There should only exist necessary files, like raids.dat and chunks.dat.

Observed Result

There is existing some files named <structure name>_index.dat., like EndCity_index.dat, Fortress_index.dat, Mansion_index.dat. Their content has two long array tag All and Remaining, but always be empty.