Remove unneeded hardcoding of REDIS_ENABLED

This keeps things consistent with the live environment and also how we
do it for the admin app where it is entirely up to environment variables
whether redis is enabled or not. This changes nothing in terms of
functionality as currently in our environment variables redis is enabled
for the API in staging.

app/config.py

@@ -481,7 +481,6 @@ class Staging(Config):
     FROM_NUMBER = 'stage'
     API_RATE_LIMIT_ENABLED = True
     CHECK_PROXY_HEADER = True
-    REDIS_ENABLED = True
 
 
 class Live(Config):
@@ -523,7 +522,6 @@ class Sandbox(CloudFoundryConfig):
     LETTERS_SCAN_BUCKET_NAME = 'cf-sandbox-letters-scan'
     INVALID_PDF_BUCKET_NAME = 'cf-sandbox-letters-invalid-pdf'
     FROM_NUMBER = 'sandbox'
-    REDIS_ENABLED = False
 
 
 configs = {