Update packages build instructions for Buster.

wiki/src/contribute/release_process/perl5lib.mdwn

@@ -70,8 +70,7 @@ Commit `debian/changelog`:
         git commit debian/changelog \
             -m "$(echo "$(dpkg-parsechangelog -SSource) ($(dpkg-parsechangelog -SVersion))\n\nGit-Dch: Ignore\n")"
 
-Build a Debian package (use a Stretch/amd64 chroot with `stretch-backports`
-enabled):
+Build a Debian package (use a Buster/amd64 chroot):
 
     gbp buildpackage
 

wiki/src/contribute/release_process/persistence-setup.mdwn

@@ -79,8 +79,8 @@ Commit `debian/changelog`:
         git commit debian/changelog \
             -m "$(echo -e "$(dpkg-parsechangelog -SSource) ($(dpkg-parsechangelog -SVersion))\n\nGit-Dch: Ignore\n")"
 
-Build a Debian package (use a Stretch/amd64 chroot, that has
-`stretch-backports` enabled, `sid` sources enabled and pinned low,
+Build a Debian package (use a Buster/amd64 chroot that has
+`sid` sources enabled and pinned low,
 and on top of that: either tails-perl5lib
 installed or the Tails APT repository configured):
 

wiki/src/contribute/release_process/tails-iuk.mdwn

@@ -102,8 +102,8 @@ Commit `debian/changelog`:
     git commit debian/changelog \
         -m "$(echo -e "$(dpkg-parsechangelog -SSource) ($(dpkg-parsechangelog -SVersion))\n\nGit-Dch: Ignore\n")"
 
-Build a Debian package (use a Stretch/amd64 chroot, that has
-`stretch-backports` enabled and on top of that: either tails-perl5lib
+Build a Debian package (use a Buster/amd64 chroot, that has
+either tails-perl5lib
 installed or the Tails APT repository configured):
 
     gbp buildpackage && \