Remove “End-user plans” feature (SaaS) - Phase 1

Accounts using this feature in SaaS were notified and asked to use the "edge limiting" policy instead.

We plan to remove this feature in 2 phases:
PHASE 1 Done in THREESCALE-2709
1a. Hide the "End User Plans" options from the UI

• Hide the "End User Plans" checkbox and description from Audience -> Settings-Usage Rules.
• Hide the row for "User Plans" feature and description from Audience -> Developer Portal -> Feature Visibility.

1b. Deactivate "End User Plans" for all the accounts with this feature enabled.

– Wait a reasonable time –

PHASE 2 Done in THREESCALE-2490
2a. Remove "End User Plans" feature from 3scale APIs.
2b. Completely remove "End User Plans" from the code