treewide: correct several "up-to-date" to "up to date"

Follow the Oxford style, which says to use "up-to-date" before the noun,
but "up to date" after it. Don't change plumbing (specifically
send-pack.c, but transport.c (git push) also has the same string).

This was produced by grepping for "up-to-date" and "up to date". It
turned out we only had to edit in one direction, removing the hyphens.

Fix a typo in Documentation/git-diff-index.txt while we're there.

Reported-by: Jeffrey Manian <jeffrey.manian@gmail.com>
Reported-by: STEVEN WHITE <stevencharleswhitevoices@gmail.com>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -2080,7 +2080,7 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb)
 				_("  (use \"git branch --unset-upstream\" to fixup)\n"));
 	} else if (!ours && !theirs) {
 		strbuf_addf(sb,
-			_("Your branch is up-to-date with '%s'.\n"),
+			_("Your branch is up to date with '%s'.\n"),
 			base);
 	} else if (!theirs) {
 		strbuf_addf(sb,