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> Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>