git-pull-<username> doesn't use pgit.sh if username == login.
pgit.sh should handle that case fine now, so remove the distinction
from topdir.mk and make it in one place, i.e. pgit.sh. This has the
additional advantage that pull as done by pgit.sh conveniently uses
--autostash.
Signed-off-by: Jan Lindemann <jan@janware.com>