VIIRS L1B DNB_SENZ file_key

[wjsharpe]

Describe the bug
The DNB_SENZ dataset in the viirs_l1b reader uses 'geolocation_data/solar_zenith' as the file_key when it should be using 'geolocation_data/sensor_zenith'

Environment Info:

• Readers and writers dependencies (when relevant): viirs_l1b

Additional context
DNB_SENZ has name as 'dnb_satellite_zenith_angle' which leads me to believe the file_key should be sensor zenith not solar zenith. Additionally DNB_SZA is already pointing at 'geolocation_data/solar_zenith' for the same file type so as it is currently setup DNB_SENZ and DNB_SZA are duplicates.