Drop overwritten key

[kaapstorm]

secrets.yml gives two values for "legacy_namespace" for "KSPLICE_ACTIVATION_KEY". PyYAML overwrites the first value with the second value:

>>> import yaml
>>> secrets = """
- name: KSPLICE_ACTIVATION_KEY
  legacy_namespace: localsettings_private
  legacy_namespace: secrets
- name: MAPBOX_ACCESS_TOKEN
  legacy_namespace: localsettings_private
  default: ''
"""
>>> yaml.safe_load(secrets)
[{'name': 'KSPLICE_ACTIVATION_KEY',
  'legacy_namespace': 'secrets'},
 {'name': 'MAPBOX_ACCESS_TOKEN',
  'legacy_namespace': 'localsettings_private',
  'default': ''}]

This change just removes the first (unused) value.