[Deprecated Component Removal] Figure Block (#2858)

Closes #1902 
All instances of this component have been removed on prod as per [this comment](#1902 (comment)), so removing it from models and custom blocks can be safely done on this pr.

## Checklist

**Changes in Models:**
- [x] Did I update or add new fake data?

network-api/networkapi/wagtailpages/customblocks.py

@@ -130,23 +130,6 @@ class Meta:
         template = 'wagtailpages/blocks/image_text_mini.html'
 
 
-class FigureBlock(blocks.StructBlock):
-    figure = AlignedImageBlock()
-    caption = blocks.CharBlock(
-        required=False,
-        help_text='Please remember to properly attribute any images we use.'
-    )
-    url = blocks.CharBlock(
-        required=False,
-        help_text='Optional URL that this figure should link out to.',
-    )
-
-    class Meta:
-        icon = 'picture'
-        template = 'wagtailpages/blocks/figure_block.html'
-        group = 'Deprecated'
-
-
 class FigureBlock2(blocks.StructBlock):
     image = ImageChooserBlock()
     caption = blocks.CharBlock(