Remove big_number import from table component

Looks like this was added in:

4a226a7a29

...and used in the spark_bar_field macro. That
macro was removed in:

89b88ee4cb

..but the import was missed out.

app/templates/components/table.html

@@ -1,5 +1,3 @@
-{% from "components/big-number.html" import big_number %}
-
 {% macro mapping_table(caption='', field_headings=[], field_headings_visible=True, caption_visible=True, equal_length=False) -%}
   <table class="table table-font-xsmall">
     <caption class="heading-medium table-heading{{ ' govuk-visually-hidden' if not caption_visible}}">