[BUGFIX] Fix wrong eval removal on TCA datetime migration

[helsner]

Resolves: #4137

[helsner]

have to fix this, right now its just the broken test

[simonschaufi]

What exactly is the bug here? I was implementing exactly the same like the core.

PS: wrongful has a different meaning than "wrong".

[helsner]

The issue is that we cannot remove the required eval within this rector.
We have one for the Datetime Migration and one for the required => true migration
But if the Datetime Migration runs before the eval => required to required => true one, then the value is getting kicked.
eval => null has the same behavior, but we handle it properly and the Nullable TCA Rector does its job afterwards