Remove apply_deferred example

[stepancheg]

Objective

Re this comment: #11141 (comment)

Since #9822, Bevy automatically inserts apply_deferred between systems with dependencies where needed, so manually inserted apply_deferred doesn't to anything useful, and in current state this example does more harm than good.

Solution

The example can be modified with removal of automatic apply_deferred insertion, but that would immediately upgrade this example from beginner level, to upper intermediate. Most users don't need to disable automatic sync point insertion, and remaining few who do probably already know how it works.

CC @hymm

[joseph-gio]

I agree, let's get rid of this. This will be stored in git so we can always bring it back and adapt it if we want to make an example aimed at power users.