{domain_export} has more than one primary key; can't install on SQLite

Trying to install DA via Drush on a site using a SQLite database results in the following:

~> drush --uri=http://spaces.test/ en domain
The following extensions will be enabled: domain
Do you really want to continue? (y/n): y
WD php: PDOException: SQLSTATE[HY000]: General error: 1 table "domain_export" has more than one primary key:   [error]
CREATE TABLE {domain_export} (
domain_id INTEGER PRIMARY KEY AUTOINCREMENT, 
machine_name VARCHAR(255) NOT NULL DEFAULT '', 
 PRIMARY KEY (machine_name)
);
; Array
(
)
 in db_create_table() (line 2684 of /Users/garrett/Sites/spaces.test/www/includes/database/database.inc).

Since this is currently happening even in the 7.x-3.3 release but there don't appear to be any other issues about this, I'm betting this isn't a problem when MySQL is used… But at any rate, the relevant bit from hook_schema() looks like this:

  $schema['domain_export'] = array(
    'description' => 'Stores canonical machine names for domains.',
    'fields' => array(
      'domain_id' => array('type' => 'serial', 'not null' => TRUE, 'description' => 'Domain id. Automatic master key.'),
      'machine_name' => array('type' => 'varchar', 'length' => '255', 'not null' => TRUE, 'default' => '', 'description' => 'The machine name for this domain.')),
    'primary key' => array('machine_name'),
    'indexes' => array(
      'domain_id' => array('domain_id')
    ),
  );

So yeah, since the serial field will already be the primary key, we can't make another one.

Possible patch attached.