t: change which user is deleted from association_table

[cmoussa1]

Problem

There is a test in t1023-flux-account-banks.t that makes sure the default bank of a user is updated when one of their user/bank rows is deleted from the database by removing it in the test prior, but the wrong user is deleted.

---

This PR just changes which user is deleted in t1023-flux-account-banks.t.

[cmoussa1]

The test continued to pass because the grep check was lazy (and my fault); grep -w "username: user5015\|bank: F\|default_bank: F" new_default_bank.out was checking for a whole-word match for one of the patterns instead of all three. I changed this grep check to be more strict and check that all three were present.

Setting MWP here