(ArcGIS API for Python) Delete fields from a feature layer using the python API

Sample.py

import arcgis
from arcgis.gis import GIS

# Provide credentials to the GIS object.
gis = GIS(username="username", password= "password")

#Get the id of the hosted feature layer
item = gis.content.get("id of feature layer")

#Get the feature layer itself
fl = item.layers[0]

#This is the JSON structure you need to pass in so that it knows what field to delete. 
# https://developers.arcgis.com/rest/services-reference/delete-from-definition-feature-layer-.htm
json = {
    "fields" : [
    {
      "name" : "POP90_SQMI"
    }
  ]
}

result = fl.manager.delete_from_definition(json)
print(result)