patch 9.1.1678: Amiga: cannot handle large undo files

patch 9.1.1678: Amiga: cannot handle large undo files

Problem:  Amiga: cannot handle large undo files
Solution: Remove the existing restriction as it was only valid for
          classic Amiga (Damien Lejay).

It seems that this block was only relevant for classic AmigaOS (< 32K
alloc limit). And it seems to no longer apply: AmigaOS 4.0 switched to
a slab allocator memory system.

closes: #18072

Signed-off-by: Damien Lejay <damien@lejay.be>
Signed-off-by: Christian Brabandt <cb@256bit.org>