prefer Essentials over Removals in ordering score

prefer Essentials over Removals in ordering score

Doing Removes early is good to have them out of the way, so they
don't break 'Inst' or 'Conf' chains, but scoring them above Essentials
means that we end up upgrading (many) less important packages before
we handle big stuff like libc6 or debconf which not only fails if those
less important packages have unannounced (strict) dependencies, but also
leads to having these packages unconfigured for a long time triggering
bugs in maintainer scripts for no good reason (#708831).

So this commits sets the default value for remove scores to 100, which
is below the one for essentials (200) and a lot lower than the previous
default value (500).