For anyone having the same problem of not being able to Uncheck the box for ‘Show Google Maps Link’ in Venues, I was able to track down the bug and offer a solution:
You can find these changes at line 141 of /wp-content/plugins/the-events-calendar/admin-views/venue-meta-box.php.
To fix the behavior, make the following change [at line 141] from:
$google_map_link_toggle = ( get_post_status($postId) != 'auto-draft' || get_post_meta( $postId, '_VenueShowMapLink', true ) !== 'false' ) ? true : false;
To the following:
$google_map_link_toggle = ( get_post_status($postId) != 'auto-draft' && get_post_meta( $postId, '_VenueShowMapLink', true ) !== 'false' ) ? true : false;
The original code always evaluated to true, which consistently set the checkbox to be “checked”, regardless of the _VenueShowMapLink post meta value in the database.
Tested against The Events Calendar v3.4.1 and WordPress v3.8.1 using Twenty Twelve v1.3.