Remove primary key GitCommitId

The table already has a Created column, and that's the column we use to sort on.

config/sql/se/GitCommits.sql

@@ -1,9 +1,7 @@
 CREATE TABLE `GitCommits` (
-  `GitCommitId` int(10) unsigned NOT NULL AUTO_INCREMENT,
   `EbookId` int(10) unsigned NOT NULL,
   `Created` datetime NOT NULL,
   `Message` text NOT NULL,
   `Hash` char(40) NOT NULL,
-  PRIMARY KEY (`GitCommitId`),
   KEY `index1` (`EbookId`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;