remove spectra_utils (#616)

* remove spectra_utils. move to astrodb_utils

* add mode to PK for spectra

Author: kelle

simple/schema.yaml

@@ -1069,6 +1069,7 @@ tables:
       datatype: string
       length: 30
       description: Instrument mode; links to Instruments table
+      nullable: false
     - name: observation_date
       "@id": "#Spectra.observation_date"
       datatype: timestamp
@@ -1102,6 +1103,7 @@ tables:
         columns: 
         - "#Spectra.source"
         - "#Spectra.regime"
+        - "#Spectra.mode"
         - "#Spectra.observation_date"
         - "#Spectra.reference"
     constraints: