A case insensitive search for the word companylogoenable shows that it is present only in reporting/includes/pdf_report.inc among the core FA files. The class member is populated inside the class method Info() only.
A similar search into the extensions shows that the custom report extensions set it from within the reports as in:
rep_annual_balance_breakdown/reporting/rep_annual_balance_breakdown.php
rep_annual_expense_breakdown/reporting/rep_annual_expense_breakdown.php
rep_cash_flow_statement/reporting/rep_cash_flow_statement.php
In the above files, the following code ensues:
..
..
$companylogoenable = true;
..
..
$rep->Info($params, $cols, $headers, $aligns, $cols2, $headers2, $aligns2, $companylogoenable, $footerenable, $footertext);
$rep->SetHeaderType('Header3');
..
..
The dummy empty class method Header1() is present in reporting/includes/class.pdf.inc and not defined in the pdf_report.inc file.
The class method Header1() is defined in the TCPDF class in reporting/includes/tcpdf.php.