Revert "Configure regional mirrors for our jobs"

Because /etc/nodepool directory doesn't exists on our zuul workers any
more. Remove this logic in favor of refactoring.

This reverts commit 2d9aab97828645e1bbae65ac481fc1dec4baf222.

Change-Id: Ie799942a8bf6e2558d6114f6418eb0b88ed40762
1 file changed