Fix variable dump in ACH customer error message when retrying a payment

[rafaelzaleski]

Fixes #3991

Changes proposed in this Pull Request:

This PR removes the variable dump in the ACH customer error message when retrying a payment.

Testing instructions

1. Reproduce the bug in develop by following the instructions in ACH: Raw variable dump appears in customer error message when retrying a payment #3991.
2. Switch to this PR and repeat the steps in ACH: Raw variable dump appears in customer error message when retrying a payment #3991.
3. The customer error message should no longer contain the variable found in step 1.

---

• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Changelog entry

• This Pull Request does not require a changelog entry. (Comment required below)

Fix customer error message when retrying a payment with ACH.

Comment

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[rafaelzaleski]

The charge_exceeds_source_limit error is intended for merchants, not shoppers. I’ve created #4046 to refactor the WC_Stripe_Exception class to better handle the messages we display for shoppers and merchants.