models: remove TiDB embedded driver support

Users should all start tidb-server process and connect to it as if
it is a MySQL server with MySQL drivers.

conf/app.ini

@@ -59,11 +59,11 @@ EXPLORE_PAGING_NUM = 20
 ISSUE_PAGING_NUM = 10
 ; Number of maximum commits showed in one activity feed
 FEED_MAX_COMMIT_NUM = 5
-; Value of `theme-color` meta tag, used by Android >= 5.0
+; Value of "theme-color" meta tag, used by Android >= 5.0
 ; An invalid color like "none" or "disable" will have the default style
 ; More info: https://developers.google.com/web/updates/2014/11/Support-for-theme-color-in-Chrome-39-for-Android
 THEME_COLOR_META_TAG = `#ff5343`
-; Max size of files to be displayed (defaults is 8MiB)
+; Max size in bytes of files to be displayed (default is 8MB)
 MAX_DISPLAY_FILE_SIZE = 8388608
 
 [ui.admin]
@@ -106,12 +106,12 @@ LOCAL_ROOT_URL = %(PROTOCOL)s://%(HTTP_ADDR)s:%(HTTP_PORT)s/
 DISABLE_SSH = false
 ; Whether use builtin SSH server or not.
 START_SSH_SERVER = false
-; Domain name to be exposed in clone URL
+; Domain name to be exposed in SSH clone URL
 SSH_DOMAIN = %(DOMAIN)s
+; Port number to be exposed in SSH clone URL
+SSH_PORT = 22
 ; Network interface builtin SSH server listens on
 SSH_LISTEN_HOST = 0.0.0.0
-; Port number to be exposed in clone URL
-SSH_PORT = 22
 ; Port number builtin SSH server listens on
 SSH_LISTEN_PORT = %(SSH_PORT)s
 ; Root path of SSH directory, default is '~/.ssh', but you have to use '/home/git/.ssh'.
@@ -157,7 +157,7 @@ RSA     = 2048
 DSA     = 1024
 
 [database]
-; Either "mysql", "postgres" or "sqlite3", it's your choice
+; Either "mysql", "postgres" or "sqlite3", you can connect to TiDB with MySQL protocol
 DB_TYPE = mysql
 HOST = 127.0.0.1:3306
 NAME = gogs
@@ -268,6 +268,7 @@ GC_INTERVAL_TIME = 86400
 SESSION_LIFE_TIME = 86400
 
 [picture]
+; Path to store user uploaded avatars
 AVATAR_UPLOAD_PATH = data/avatars
 ; Chinese users can choose "duoshuo"
 ; or a custom avatar source, like: http://cn.gravatar.com/avatar/