docs/process: branching-checklist: Remove section about the cambridge colo

The cambridge colo was internal to Citrix (now Cloud) and hasn't been used
by the community for a while.

So remove the section.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Acked-by: George Dunlap <george.dunlap@cloud.com>
Reviewed-by: Henry Wang <Henry.Wang@arm.com>

----
    Changes in v2:
        - Add George's acked-by
        - Add Henry's reviewed-by

docs/process/branching-checklist.txt

@@ -42,12 +42,6 @@ ov=4.0
     OSSTEST_CONFIG=production-config ./mg-branch-setup xen-$v-testing bisect
     OSSTEST_CONFIG=production-config ./mg-branch-setup qemu-upstream-$v-testing bisect
 
-# make branches etc. in Cambridge osstest
-    ssh osstest@osstest.xs.citrite.net
-    cd testing.git
-    OSSTEST_CONFIG=production-config-cambridge ./mg-branch-setup xen-$v-testing bisect
-    OSSTEST_CONFIG=production-config-cambridge ./mg-branch-setup qemu-upstream-$v-testing bisect
-
 * add branch to osstest
     Add both qemu-upstream-$v-testing and xen-$v-testing to BRANCHES in cr-for-branches
     git add -p