Remove GitHub OAuth fork from the plugins list

We are using our own fork of this plugin until the change to allow
teams by slug is merged into the main repo:
jenkinsci/github-oauth-plugin#124

Including this plugin in the list causes the build to fail because
it's been built manually.

docker/plugins.txt

@@ -29,7 +29,6 @@ git-server:1.9
 github:1.33.1
 github-api:1.122
 github-branch-source:2.10.1
-github-oauth:0.34-SNAPSHOT (private-53e10daa-sam)
 handlebars:1.1.1
 jackson2-api:2.12.1
 jdk-tool:1.5