Give the session table a normal `id` column as a primary key

Summary:
Ref T4310. Ref T3720. Two major things are going on here:

- I'm making this table work more like a standard table, which, e.g., makes `delete()` simpler to implement.
- Currently, the primary key is `(userPHID, type)`. I want to get rid of this, issue unlimited sessions, and GC old sessions. This means we can't have a unique key on `(userPHID, type)` anymore. This removes it as the primary key and adds it as a normal key instead. There's no functional change -- the code to generate sessions guarantees that it will never write duplicate rows or write additional rows -- but allows us to drop the `-1`, `-2` qualifiers in the future.
- Also of note, our task is made far simpler here because MySQL will automatically assign values to new `AUTO_INCREMENT` columns, so we don't have to migrate to get real IDs.

Test Plan: Ran migrations, verified table looked sane. Logged out, logged in.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3720, T4310

Differential Revision: https://secure.phabricator.com/D7975

resources/sql/autopatches/20140115.auth.1.id.sql

···
+ALTER TABLE {$NAMESPACE}_user.phabricator_session
+  DROP PRIMARY KEY;
+
+ALTER TABLE {$NAMESPACE}_user.phabricator_session
+  ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY FIRST;
+
+ALTER TABLE {$NAMESPACE}_user.phabricator_session
+  ADD KEY `key_identity` (userPHID, type);

src/applications/auth/storage/PhabricatorAuthSession.php

···
 
   public function getConfiguration() {
     return array(
-      self::CONFIG_IDS => self::IDS_MANUAL,
       self::CONFIG_TIMESTAMPS => false,
     ) + parent::getConfiguration();
   }
···
 
   public function getIdentityObject() {
     return $this->assertAttached($this->identityObject);
-  }
-
-  public function delete() {
-    // TODO: We don't have a proper `id` column yet, so make this work as
-    // expected until we do.
-    queryfx(
-      $this->establishConnection('w'),
-      'DELETE FROM %T WHERE sessionKey = %s',
-      $this->getTableName(),
-      $this->getSessionKey());
-    return $this;
   }
 
 /* -(  PhabricatorPolicyInterface  )----------------------------------------- */