dev/core#2073 Fix use of legacy leaky method in tested code

dev/core#2073 Fix use of legacy leaky method in tested code

Overview
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Fix use of legacy leaky method in tested code

Before
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dao->query()

After
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CRM_Core_DAO::executeQuery()

Technical Details
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This is too low volume to really leak but it uses the leaky legacy method and
has test cover in

CRM_Import_DataSource_CsvTest.testToCsv with data set #0
CRM_Import_DataSource_CsvTest.testToCsv with data set #1
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