MM-34080: Removing sqlite entirely (#17188)

* MM-34080: Removing sqlite entirely

The initial commit missed removing this blank import.
So the library still remained in our vendor directory.
Removing it for good now.

Bye bye sqlite.

https://mattermost.atlassian.net/browse/MM-34080

* fix go.mod

store/sqlstore/store_test.go

@@ -13,7 +13,6 @@ import (
 	"github.com/go-sql-driver/mysql"
 	"github.com/lib/pq"
 	"github.com/mattermost/gorp"
-	_ "github.com/mattn/go-sqlite3"
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"