[handbook] remove two links from the zfs links page

These two links just go to ads pages. For the "evil tuning guide" I was
able to find find some pages with a similar title but they are
years old and don't give current advice. For "ZFS Best Practices Guide"
there are many variants and none seemed particularly worthwhile to link.

Reported by: Jakob Rönnbäck <jakob.ronnback@me.com>