RHIDP-5765 comment out references to GitHub Enterprise (#900)

Signed-off-by: Fabrice Flore-Thébault <ffloreth@redhat.com>

modules/authentication/proc-enabling-authentication-with-github.adoc

@@ -55,7 +55,7 @@ TIP: If you plan to make changes using the GitHub API, ensure that `Read and wri
 +
 `AUTH_GITHUB_APP_ID`:: Enter the saved **App ID**.
 `AUTH_GITHUB_CLIENT_ID`:: Enter the saved **Client ID**.
-`GITHUB_HOST_DOMAIN`:: Enter your GitHub host domain: `github.com` unless you are using GitHub Enterprise.
+//`GITHUB_HOST_DOMAIN`:: Enter your GitHub host domain: `github.com` unless you are using GitHub Enterprise.
 `GITHUB_ORGANIZATION`:: Enter your GitHub organization name, such as `__<your_github_organization_name>__'.
 `GITHUB_ORG_URL`:: Enter `$GITHUB_HOST_DOMAIN/$GITHUB_ORGANIZATION`.
 `GITHUB_CLIENT_SECRET`:: Enter the saved **Client Secret**.
@@ -145,6 +145,7 @@ auth:
         callbackUrl: __<your_intermediate_service_url/handler>__
 ----
 
+////
 `enterpriseInstanceUrl`::
 Your GitHub Enterprise URL.
 Requires you defined the `GITHUB_HOST_DOMAIN` secret in the previous step.
@@ -158,6 +159,7 @@ auth:
       production:
         enterpriseInstanceUrl: ${GITHUB_HOST_DOMAIN}
 ----
+////
 
 [TIP]
 ====