Remove "mysql.implementation" configuration

Summary:
Ref T11044. Fixes T10931. This option has essentially never been useful for anything, and we've picked the best implementation for a long time (MySQLi if available, MySQL if not).

I am not aware of any reason to ever set this manually. If someone comes up with some bizarre but legitimate use case that I haven't thought of, we can modularize it.

Test Plan: Browsed around. Grepped for `mysql.implementation`.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10931, T11044

Differential Revision: https://secure.phabricator.com/D16909

src/applications/config/check/PhabricatorExtraConfigSetupCheck.php

···
       'maniphest.priorities.unbreak-now' => $dashboard_reason,
       'maniphest.priorities.needs-triage' => $dashboard_reason,
 
+      'mysql.implementation' => pht(
+        'Phabricator now automatically selects the best available '.
+        'MySQL implementation.'),
     );
 
     return $ancient_config;

src/applications/config/option/PhabricatorMySQLConfigOptions.php

···
             'Phabricator chooses which database to connect to through a '.
             'swappable configuration provider. You almost certainly do not '.
             'need to change this.')),
-      $this->newOption(
-        'mysql.implementation',
-        'class',
-        (extension_loaded('mysqli')
-          ? 'AphrontMySQLiDatabaseConnection'
-          : 'AphrontMySQLDatabaseConnection'))
-        ->setLocked(true)
-        ->setBaseClass('AphrontMySQLDatabaseConnectionBase')
-        ->setSummary(
-          pht('Configure database connection class.'))
-        ->setDescription(
-          pht(
-            'Phabricator connects to MySQL through a swappable abstraction '.
-            'layer. You can choose an alternate implementation by setting '.
-            'this option. To provide your own implementation, extend '.
-            '`%s`. It is very unlikely that you need to change this.',
-            'AphrontMySQLDatabaseConnectionBase')),
       $this->newOption('storage.default-namespace', 'string', 'phabricator')
         ->setLocked(true)
         ->setSummary(

src/applications/console/plugin/DarkConsoleServicesPlugin.php

···
       // For each SELECT query, go issue an EXPLAIN on it so we can flag stuff
       // causing table scans, etc.
       if (preg_match('/^\s*SELECT\b/i', $entry['query'])) {
-        $conn = PhabricatorEnv::newObjectFromConfig(
-          'mysql.implementation',
-          array($entry['config']));
+        $conn = PhabricatorDatabaseRef::newRawConnection($entry['config']);
         try {
           $explain = queryfx_all(
             $conn,

src/infrastructure/cluster/PhabricatorDatabaseRef.php

···
       'timeout' => $default_timeout,
     );
 
-    return PhabricatorEnv::newObjectFromConfig(
-      'mysql.implementation',
-      array(
-        $spec,
-      ));
+    return self::newRawConnection($spec);
+  }
+
+  public static function newRawConnection(array $options) {
+    if (extension_loaded('mysqli')) {
+      return new AphrontMySQLiDatabaseConnection($options);
+    } else {
+      return new AphrontMySQLDatabaseConnection($options);
+    }
   }
 
 }

src/infrastructure/storage/lisk/PhabricatorLiskDAO.php

···
       'mysql.configuration-provider',
       array($this, $mode, $namespace));
 
-    return PhabricatorEnv::newObjectFromConfig(
-      'mysql.implementation',
+    return PhabricatorDatabaseRef::newRawConnection(
       array(
-        array(
-          'user'      => $conf->getUser(),
-          'pass'      => $conf->getPassword(),
-          'host'      => $conf->getHost(),
-          'port'      => $conf->getPort(),
-          'database'  => $database,
-          'retries'   => 3,
-          'timeout' => 10,
-        ),
+        'user' => $conf->getUser(),
+        'pass' => $conf->getPassword(),
+        'host' => $conf->getHost(),
+        'port' => $conf->getPort(),
+        'database' => $database,
+        'retries' => 3,
+        'timeout' => 10,
       ));
   }
 

src/infrastructure/storage/management/PhabricatorStorageManagementAPI.php

···
     $database = $this->getDatabaseName($fragment);
     $return = &$this->conns[$this->host][$this->user][$database];
     if (!$return) {
-      $return = PhabricatorEnv::newObjectFromConfig(
-      'mysql.implementation',
-      array(
+      $return = PhabricatorDatabaseRef::newRawConnection(
         array(
           'user'      => $this->user,
           'pass'      => $this->password,
···
           'database'  => $fragment
             ? $database
             : null,
-        ),
-      ));
+        ));
     }
     return $return;
   }