[BUGFIX] Sphinx breaks extension "extension_uploader"

Invalid category "service" instead of "services" in ext_emconf.php.

Change-Id: I8ddf827d9ee53463daf8664877c352499b19b595
Fixes: #54739
Reviewed-on: https://review.typo3.org/26641
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers