[TASK] Remove dummy files from ext:indexed_search

* The pi1 script still lives as dummy file since the addPItoST43
  registration fails otherwise.
* modfunc1 and modfunc2 class files still live as dummy files as
  the sub-sub module handling in core fails otherwise.

Change-Id: I21b92a07e7ff83cd1dd3f12b0e15bef7f84691e9
Resolves: #47852
Related: #47756
Releases: 6.2
Reviewed-on: https://review.typo3.org/20442
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters