Remove programatically Service columns

[Martouta]

Ignore some columns in Service through the Rails 5 way (ignored_columns) instead of the old way (overriding the columns class method).
This is part of THREESCALE-2635 and follows the investigation done in the comments of THREESCALE-2715

Explanation of each column being ignored

• act_as_product was ignored before this PR. The reason is we initially created it while we were developing the APIAP feature but then we decided to not do it this was and this column is not used at all. Neither in SaaS nor in on-prem.
• end_user_registration_required was ignored when the whole code of the end user and end user plan deprecated feature was removed.
• default_end_user_plan_id was ignored when the whole code of the end user and end user plan deprecated feature was removed.
• oneline_description is ignored because it is not used in the code and the only service whose tenant is not scheduled for deletion that has this value different than null is incomplete and has not been updated for 2 years.
• txt_api is ignored because it is not used at all in the code and everybody has null in the DB.
• txt_features is ignored because is not used in the code and in the DB the only Service that has it filled is from a tenant scheduled_for_deletion.
• infobar is ignored because there was only once reference in the code in that code it is hidden from the customer and with a comment requesting removing it completely. I also removed that code in this PR.
• draft_name is ignored because it is not used.
• display_provider_keys is ignored because there is only one service with value true which has state incomplete and description not used and there is only one reference in the code, which I removed too after asking @thomasmaas if it was ok to remove that.
• credit_card_support_email is ignored because it is not used.
• admin_support_email was already ignored from some time ago.
• tech_support_email was already ignored from some time ago.

Columns not ignored/removed because I am not sure

txt_support and terms for what I explained in this comment

[guicassolato]

Nice clean-up!