loader_package: Fix sentry setup key name
loader_package: Fix sentry setup key name

Their sentry_name key is 'loader_core'.
Thus, there is no need to duplicate keys.
2 correct key entries are enough for all loader packages.

SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site