copies-sdc: no longer use revlogv2 in `test-copies-in-changeset.t`

We only need changelog-v2 and its usage is automatically inferred. So we can
simplify the test by dropping this.

This is important to test future simplification of the update process in the
coming changesets.

tests/test-copies-in-changeset.t

@@ -434,14 +434,12 b' downgrading'
   $ cat << EOF > .hg/hgrc
   > [format]
   > exp-use-copies-side-data-changeset = no
-  > [experimental]
-  > revlogv2 = enable-unstable-format-and-corrupt-my-data
   > EOF
   $ hg debugupgraderepo --run --quiet --no-backup > /dev/null
   $ hg debugformat -v | egrep 'format-variant|revlog-v2|copies-sdc|changelog-v2'
   format-variant     repo config default
   copies-sdc:          no     no      no
-  revlog-v2:          yes    yes      no
+  revlog-v2:           no     no      no
   changelog-v2:        no     no      no
   $ hg debugsidedata -c -- 0
   $ hg debugsidedata -c -- 1