HaikuDepot: Fix usage of std::remove.

That's right kids, std::remove doesn't (and can't) actually remove
things from containers! Instead you have to pass its results into
container::erase in order to do anything at all.

Fixes #17579, and in my testing at least, the strange crashes
and heap corruptions.

HaikuDepot: Remove Custom List

Further removal of the use of custom list class;
this time with the generic undo functionality.

Relates To #15534

Change-Id: I804a31abc07f42f4f1695562b6f948feb465db0c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3739
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

use .IsSet() instead if .Get() != NULL

Change-Id: Ia2b7a719fd398e78cc3b11d4f7b02cb81179f65f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3488
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

HaikuDepot: Base-classes for generic undo/redo support.

I plan to use these in the text view and editor framework.

HaikuDepot: Base-classes for generic undo/redo support.

I plan to use these in the text view and editor framework.