[12.x] Remove obsolete driver option

[AhmedAlaa4611]

Continuation of laravel/laravel#6395 and laravel/laravel#6591

[taylorotwell]

We will need to fix the comment formatting.

[rodrigopedra]

Cascading comment lines that keep following line with 3 characters less than the previous:

/*
|--------------------------------------------------------------------------
| Cache Key Prefix
|--------------------------------------------------------------------------
|
| When utilizing the database, memcached, Redis, and DynamoDB cache
| stores, there might be other applications using the same cache.
| As such, you may prefix every cache key to avoid collisions.
|
*/