Multisite: Remove the redundant blog_versions table.

As part of the Multisite installation process, a `blog_versions` table is created. This table is never read from (except immediately prior to updating it), it's only ever inserted into or updated. It is not used to determine which blogs need to be upgraded.
This table was introduced in 3.0 when the WPMU schema was merged #11644 and it appears the table has never been used in core and is therefore redundant and may as well be removed.

Props johnbillion, nacin, ryan, johnjamesjacoby, whyisjake.

Fixes #19755. See #41685.


Built from https://develop.svn.wordpress.org/trunk@46194


git-svn-id: http://core.svn.wordpress.org/trunk@46006 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/schema.php

@@ -261,13 +261,6 @@ CREATE TABLE $wpdb->posts (
 	KEY domain (domain(50),path(5)),
 	KEY lang_id (lang_id)
 ) $charset_collate;
-CREATE TABLE $wpdb->blog_versions (
-	blog_id bigint(20) NOT NULL default '0',
-	db_version varchar(20) NOT NULL default '',
-	last_updated datetime NOT NULL default '0000-00-00 00:00:00',
-	PRIMARY KEY  (blog_id),
-	KEY db_version (db_version)
-) $charset_collate;
 CREATE TABLE $wpdb->blogmeta (
 	meta_id bigint(20) unsigned NOT NULL auto_increment,
 	blog_id bigint(20) NOT NULL default '0',