bank-account: remove redundant iteration (#1611)
bank-account: remove redundant iteration (#1611)

If a solution passes after 1 pass of 1000 concurrent transactions,
9 additional passes will not cause that solution to fail. These extra
passes only waste processing time, both for the student and for
contributors.
N-Parsons/exercism-python,jmluy/xpython,exercism/xpython,jmluy/xpython,exercism/xpython,exercism/python,behrtam/xpython,behrtam/xpython,exercism/python,smalley/python,N-Parsons/exercism-python,smalley/python