Add a HEADER_X_POWERED_BY definition, similar to CLUSTER_HEADER_X_POWERED_BY, to remove the x_powered_by header from eZ Publish.

HEADER_X_POWERED_BY set to false -> No header at all
HEADER_X_POWERED_BY set to false -> Powered by eZ Publish

Setting that header to false, it will be up to the customer to set the expose_php to OFF to hide the PHP version he is using.