chore: switch database engine to sqlite (fixes #9954) (#9965)

Switch the database from LevelDB to SQLite, for greater stability and
simpler code.

Co-authored-by: Tommy van der Vorst <tommy@pixelspark.nl>
Co-authored-by: bt90 <btom1990@googlemail.com>

cmd/syncthing/cli/utils.go

@@ -17,8 +17,6 @@ import (
 	"path/filepath"
 
 	"github.com/syncthing/syncthing/lib/config"
-	"github.com/syncthing/syncthing/lib/db/backend"
-	"github.com/syncthing/syncthing/lib/locations"
 )
 
 func responseToBArray(response *http.Response) ([]byte, error) {
@@ -133,10 +131,6 @@ func prettyPrintResponse(response *http.Response) error {
 	return prettyPrintJSON(data)
 }
 
-func getDB() (backend.Backend, error) {
-	return backend.OpenLevelDBRO(locations.Get(locations.Database))
-}
-
 func nulString(bs []byte) string {
 	for i := range bs {
 		if bs[i] == 0 {