SQLite/GPKG: turn on SQLite 'PRAGMA secure_delete=1' by default

[rouault]

unless the user specifies a value of this pragma through OGR_SQLITE_PRAGMA.

For example, Debian and Conda-Forge SQLite3 builds already turn on secure_delete. Make sure that this is done for all SQLite3 builds.

[jratike80]

I made some tests. SECURE_DELETE=ON makes deleting 5.6 million rows from a regular, non-spatial table 6 times slower, 2.5 sec vs 15 sec.
However, deleting massive amounts of data from SQLite is always very slow when tables have triggers, and that is the case with spatial geopackage tables.

Deleting a 5.6 million table with the same data as in the previous tests but now with r-tree, triggers and everything in geopackage requires this much time:
secure_delete=no 326 seconds
secure_delete=yes 370 seconds

Considerations about similar, but more compicated use case https://gis.stackexchange.com/questions/486885/better-control-cascading-triggers-in-sqlite

Note: My test was the most optimal for the regular table, a query that makes SQLite to take the fast "truncate table" road.

delete from rakennus;

[coveralls]

coverage: 69.468% (-4.0%) from 73.478%
when pulling 5e84b2d on rouault:sqlite_gpkg_secure_delete
into a8117d9 on OSGeo:master.

[rouault]

Deleting a 5.6 million table with the same data as in the previous tests but now with r-tree, triggers and everything in geopackage requires this much time:

Will be vastly improved with #11139

[rouault]

Conda-Forge SQLite3 builds already turn on secure_delete

On deeper review, was actually only true of the Linux and Mac builds. Submitted conda-forge/sqlite-feedstock#116 to do that on Windows too