Much appreciated Andy, that worked perfectly and solved my issue:
For those who stumble on the post later, here is the command to hide the bugs and leads subpanel from the Accounts panel.
$cat ./custom/Extension/modules/Accounts/Ext/Layoutdefs/custom.php
unset($layout_defs['Accounts']['subpanel_setup']['bugs']);
unset($layout_defs['Accounts']['subpanel_setup']['leads']);