[PATCH 0/4][linux-signed*] Correct source package in Built-Using control field

[dann frazier]

BugLink: https://bugs.launchpad.net/bugs/1824016

The Built-Using field hardcodes "linux" as the source package, even for the
hwe & hwe-edge packages. Correct that. Technically only the
linux-signed-hwe{-edge} packages need this fix, but I'm including patches
for linux-signed as well to prevent future occurences due to cargo-culting.

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2.20.1