Fixed source references in debian/control

Summary: It was discovered that a number of contrib/ files still reference core links. Cleaning these up...

Test Plan: N/A, as these are for documentatio purposes only: https://www.debian.org/doc/manuals/maint-guide/dreq.en.html

Reviewers: deadalnix, schancel, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1414