Simplify "git reset --hard"

Simplify "git reset --hard"

Now that the one-way merge strategy does the right thing wrt files that do
not exist in the result, just remove all the random crud we did in "git
reset" to do this all by hand.

Instead, just pass in "-u" to git-read-tree when we do a hard reset, and
depend on git-read-tree to update the working tree appropriately.

This basically means that git reset turns into

	# Always update the HEAD ref
	git update-ref HEAD "$rev"

	case "--soft"
		# do nothing to index/working tree
	case "--hard"
		# read index _and_ update working tree
		git-read-tree --reset -u "$rev"
	case "--mixed"
		# update just index, report on working tree differences
		git-read-tree --reset "$rev"
		git-update-index --refresh

which is what it was always semantically doing, it just did it in a
rather strange way because it was written to not expect git-read-tree to
do anything to the working tree.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>