Remove AlignedImageBlock from customblocks

[youriwims]

Describe the bug
The class AlignedImageBlock is still in customblocks.py but doesn't appear to be in use. This is a follow up to #2999.

To Reproduce
Steps to reproduce the behavior:

1. Go to /network-api/networkapi/wagtailpages/customblocks.py
2. Line 73 still has unused AlignedImageBlock class.

[Sharma-palak]

@youriwims ,Is this issue still open? can i take this issue ??

[Pomax]

@kristinashu can you confirm our content no longer requires this block to exist?

[kristinashu]

I checked with Youri and she has confirmed that we should remove this block.

I also checked our inventory and it isn't showing up so guess it isn't in use anywhere:

[mmmavis]

Confirmed that we can remove the block.