remove: use ctx.hasdir(f) instead of 'f in ctx.dirs()'
This speeds up 'hg remove python/README' on the Firefox repo from
2.479s to 0.664s with lazily loaded treemanifests (which is not yet in
core) and has no measurable effect on flat manifests.
#require serve killdaemons
#if windows
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
#else
$ hg clone http://localhost:$HGPORT/ copy
abort: error: Connection refused
[255]
#endif
$ 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)
[255]
$ "$TESTDIR/killdaemons.py" $DAEMON_PIDS