Cleanup customer schema, remove one (deprecated) field; add ipdb.

[dsprayberry]

Description of change

• Re-orders the fields listed in the customers.json schema file to alphabetize properties and match Recharge docs for easier long-term maintenance.
• Removes the shopify_customer_id field which has been removed by Recharge in favor of the external_customer_id object
• Adds ipdb to the dev install

Manual QA steps

• Validated object structure via direct API response
• Successful sync locally

Risks

• Users may be confused as to why this field is no longer available for selection, but fields are filtered during transform for this tap, so there's no change to request structure and it is not being returned by Recharge on this API version.

Rollback steps

• revert this branch

[dmosorast]

Once tests are updated to match the expectations, I'm good with this. Looks like the failures are happening on master as well.

[dmosorast]

Secondary approve.