IS-255: Test and remove code for creating enterprise docker image. (#14395)

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

build/README.md

@@ -2,8 +2,6 @@
 
 This folder contains some files that we use to build the `mattermost-server` using `Jenkins` and other files like privacy policy and licenses.
 
-PRs opened against the `mattermost-server` repository will use the file called `Jenkinsfile.pr`
-
 The `Dockerfile` in this folder (`Dockerfile.buildenv`) is the build environment for our current builds you can find the docker image to download [here](https://hub.docker.com/r/mattermost/mattermost-build-server/tags/) or build your own.