Update github default callback url

doc/integration/github.md

@@ -17,8 +17,7 @@ GitHub will generate an application ID and secret key for you to use.
     - Application name: This can be anything. Consider something like "\<Organization\>'s GitLab" or "\<Your Name\>'s GitLab" or something else descriptive.
     - Homepage URL: The URL to your GitLab installation. 'https://gitlab.company.com'
     - Application description: Fill this in if you wish.
-    - Authorization callback URL: 'https://gitlab.company.com/'
-    - If install from source, default callback URL is '${YOUR_DOMAIN}/import/github/callback'
+    - Default authorization callback URL is '${YOUR_DOMAIN}/import/github/callback'
 1.  Select "Register application".
 1.  You should now see a Client ID and Client Secret near the top right of the page (see screenshot).