Drop old "differential_commit" table

Summary: Ref T13276. Ref T13513. All readers and writers were removed more than a year ago; clean up the last remnants of this table.

Test Plan: Grepped for table references, found none.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13513, T13276

Differential Revision: https://secure.phabricator.com/D21281

resources/sql/autopatches/20200520.inline.03.dropcommit.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS {$NAMESPACE}_differential.differential_commit;

src/applications/differential/storage/DifferentialSchemaSpec.php

@@ -31,27 +31,6 @@ final class DifferentialSchemaSpec extends PhabricatorConfigSchemaSpec {
         'persistence' => PhabricatorConfigTableSchema::PERSISTENCE_CACHE,
       ));
 
-    // TODO: All readers and writers for this table were removed in April
-    // 2019. Destroy this table once we're sure we won't miss it.
-
-    $this->buildRawSchema(
-      id(new DifferentialRevision())->getApplicationName(),
-      'differential_commit',
-      array(
-        'revisionID' => 'id',
-        'commitPHID' => 'phid',
-      ),
-      array(
-        'PRIMARY' => array(
-          'columns' => array('revisionID', 'commitPHID'),
-          'unique' => true,
-        ),
-        'commitPHID' => array(
-          'columns' => array('commitPHID'),
-          'unique' => true,
-        ),
-      ));
-
     $this->buildRawSchema(
       id(new DifferentialRevision())->getApplicationName(),
       ArcanistDifferentialRevisionHash::TABLE_NAME,