improve missing repository error message

improve missing repository error message

Certain remote commands, when asked to do something in a
particular directory that was not actually a git repository,
would say "unable to chdir or not a git archive". The
"chdir" bit is an unnecessary detail, and the term "git
archive" is much less common these days than "git repository".

So let's switch them all to:

  fatal: '%s' does not appear to be a git repository

Signed-off-by: Jeff King <redacted>
Acked-by: Shawn O. Pearce <redacted>
Signed-off-by: Junio C Hamano <redacted>