dirstate: inline the `from_p2_removed` logic
It is used internally for compatibilty with size used in the `v1` format, but
this is the only use. So we can simply inline it.
Differential Revision: https://phab.mercurial-scm.org/D11514
#require serve
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[100]
$ test -d copy
[1]
$ "$PYTHON" "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[100]
$ killdaemons.py