SCHEMA: Drop from SHOULD to MAY to avoid validation implications

Author: effigies

src/schema/objects/columns.yaml

@@ -302,9 +302,8 @@ notch:
   display_name: Notch frequencies
   description: |
     Frequencies used for the notch filter applied to the channel, in Hz.
-    If the low and high frequencies are supplied in addition to the center
-    frequency, it is RECOMMENDED that they take the form `[low, center, high]`,
-    for example `[60, 120, 180]`.
+    If the low and high frequencies are supplied in addition to the center frequency,
+    they MAY take the form `[low, center, high]`, for example `[60, 120, 180]`.
     If no notch filter applied, use `n/a`.
   type: string
 onset: