Jenkins: Drop chroots we're not using anymor

The armhf and amd64 builds moved to a slave.

install_jenkins.yml

@@ -41,20 +41,8 @@
         - gbp_keyrings
     - role: gbp
       gbp_cowbuilder_targets:
-        - dist: sid
         - dist: buster
-        - dist: stretch
-        - dist: sid
-          arch: armhf
-          foreign: true
         - dist: buster
-          arch: armhf
-          foreign: true
-        - dist: buster
-          arch: amd64
-          foreign: true
-        - dist: buster
-          arch: arm64
           autoconf: False
           basepath: /var/cache/pbuilder/base-buster+plamo.cow
           pbuilder_options: "--dist=buster --keyring=/etc/pbuilder/keyrings/ci-repo.gpg --othermirror='deb http://ci.puri.sm/ plamoci librem5'"