The only reason why a user would want to entirely disable file indexing is because they
don't want their files indexed. This implies that if their files are already indexed,
they would like the index deleted. Ergo, disabling indexing in the KCM should delete
the index too.
This patch does that. The balooctl command-line tool offers more granular options for
disabling without deleting the index, but those should be considered expert options for
power users who know what they're doing. For users using the KCM, deleting the index
after disabling indexing makes the most sense.
BUG: 414077
FIXED-IN: 5.18.0
Depends on D25447