tests: use common obshistory_setup.sh script instead of manual setup
This is now consistent with other test-evolve-obshistory*.t tests.
Enable obsolescence to avoid the warning issue when obsmarkers are found
$ cat << EOF >> $HGRCPATH
> [experimental]
> evolution = all
> EOF
$ $TESTDIR/../contrib/check-compat-strings.sh "$TESTDIR/../hgext3rd/" "$RUNTESTDIR/.."