[OPENENGSB-2752] Removed no longer existing maven.openengsb.org repo
[OPENENGSB-2752] Removed no longer existing maven.openengsb.org repo

This no longer used repository definition produced various errors.
Though, the most critical problem was that it hides real resolvement
errors behind a 505 error.

Signed-off-by: Andreas Pieber <57efbcbb22ec0bd89955a40df26b44c340d3e38d@gmail.com>

openengsb/openengsb-root,GitHub2020/openengsb-root,openengsb/openengsb-root,GitHub2020/openengsb-root