Remove {masquerade} table and rely on session flag only

As for D8, the patch in #19 was committed and currently D7 is targeted in this issue.

History

• #822120: Get rid of masquerading as anonymous (sort of) →
• #705858: Don't create session var when not masqerading →
• #1813696: Set/unset Session flag when masquerade status changes. →

Details

• 8.x-2.x no longer supports masquerading as Anonymous. That facility required tons of custom code and hacks for little benefit. One can simply log out instead, or use a separate browser. See #1836516: Port Masquerade to D8 and rewrite + simplify it into a new 2.x series →
• The {masquerade} database table was originally introduced with the initial commit for Drupal 4.6.x: http://drupalcode.org/project/masquerade.git/history/HEAD:/masquerade.mysql
• We're setting the 'masquerading' flag on a user's session (when actively masquerading) and the flag is removed when unmasquerading.
• masquerade_init() performs a database query against {masquerade} on every page request. Studying the above historical issues reveals that this was only required to support masquerading as anonymous.

Proposed solution

1. Since masquerading as Anonymous is gone, drop the table and all queries to it entirely.