archives: always include enabled/disabled deb-src apt entries

LB_APT_SOURCE_ARCHIVES determines whether or not deb-src entries are desired to be included in apt's sources.list. here, instead of excuding them we always include them but commented out where they would previously have been excluded. this means that if a user later changes their mind and wants to make use of them all they have to do is uncomment them rather than add the necessary lines.

Gbp-Dch: Short Closes: #952929