Clean up unused {block_node_type} table and references

Problem/Motivation

Following #1535868: Convert all blocks into plugins, the node type visibility settings for a block instance are stored in that block instance's configuration file, and the {block_node_type} table is unused.

Proposed resolution

• Remove the {block_node_type} table from the node schema.
• Remove unused references to this table.
• Add the table to the list at #1860986: Drop left-over tables from 8.x

Related issues:

• #1887688: locale_update_8001() references unused block tables