Remove theme_book_admin_table and call theme('table__book_admin') 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 two options:

1. Remove theme_book_admin_table and call theme('table') instead.
2. If we really do need a separate preprocess function for the admin tables in book module, then call theme('table__book_admin') instead of theme('table') and add all our preprocess magic into template_preprocess_table__book_admin()

Remaining tasks

Decide which of the 2 options above to pursue, and do it.

User interface changes

None.

API changes

Removal of theme_book_admin_table

Related Issues

#1812684: [meta] Consolidate all table templates and add theme_hook_suggestions
#1968982: Convert book theme tables to table #type