Remove unnecessary build step (#1003)
Remove unnecessary build step (#1003)

The builder image does not need to cleanup itself, 
the whole purpose of it is to be dropped after the final artifacts are copied out.
ngoduykhanh/PowerDNS-Admin,ngoduykhanh/PowerDNS-Admin,ngoduykhanh/PowerDNS-Admin,ngoduykhanh/PowerDNS-Admin