Align impression-site-quota deduction in simulator with spec

[apasel422]

This is just a minor code reorganization in the simulator corresponding to

attribution/api.bs

Lines 1264 to 1284 in c3e21e1

	1. [=list/iterate|For each=] |impression| in |impressions|:
	1. Let |impressionSite| be |impression|'s [=impression/impression site=].
	1. Let |impressionQuotaKey| be an [=privacy budget key=]
	whose items are |epoch| and |impressionSite|.
	<p class=note>The below ensures that we do not deduct budget
	more than once from the same impression site quota
	when there are multiple impressions for the site.
	1. If |deductedImpressionQuotas| does not [=map/contain=] |impressionQuotaKey|:
	1. [=set/Append=] |deductedImpressionQuotas| with |impressionQuotaKey|.
	1. Let |currentImpressionQuotaValue| be the result of [=map/get|getting the value=] of |impressionQuotaKey|
	in the [=impression site quota per epoch=]
	with a default of the [=impression site quota per epoch=].
	1. [=map/set|Set=] the value of [=impression site quota per epoch=]\[|impressionQuotaKey|\]
	to |currentImpressionQuotaValue| − |valueDeduction|.

.