remove theme_image_style_list() and call theme('table__image_styles__list') instead

Problem/Motivation

There are way too many theme functions / template files in core. Some are similar (if not identical) and should be consolidated.

Proposed resolution

We have three options:

1. Remove theme_image_style_list and call theme('table') instead.
2. If we really do need a separate preprocess function for the admin tables in image module, then call theme('table__image_styles') instead of theme('table') and add all our preprocess magic into template_preprocess_table__image_styles()
3. If we really do need a separate preprocess function for this *single* table, then call theme('table__image_styles__list') instead of theme('table__image_styles') and do all our preprocess magic into template_preprocess_table__image_styles__list()

Remaining tasks

Decide which of the 3 options above to pursue, and do it.

User interface changes

None.

API changes

Removal of theme_image_style_list

Related Issues

#2035903: Remove theme_image_style_effects() and call theme('table__image_styles__effects') instead.
#1812684: [meta] Consolidate all table templates and add theme_hook_suggestions
#1898420: image.module - Convert theme_ functions to Twig
#1938910: Convert image theme tables to table #type