This is the default layout provided by the EzPublishLegacyBundle. To override it, you can use the following configuration:
# for instance in ezpublish.yml
# The "default" scope can be replaced by any available scope
# https://confluence.ez.no/display/EZP/Configuration#Configuration-Scope
parameters:
ezpublish_legacy.default.view_default_layout: YourBundle::pagelayout.html.twig