ls-files: clarify descriptions of status tags for -t

Much like the file selection options we tweaked in the last commit, the status tags printed with -t had descriptions that were easy to misunderstand, and for many of the same reasons. Clarify them. Also, while at it, remove the "semi-deprecated" comment for "git ls-files -t". The -t option was marked as semi-deprecated in 5bc0e247c4 ("Document ls-files -t as semi-obsolete.", 2010-07-28) because:     "git ls-files -t" is [...] badly documented, hence we point the     users to superior alternatives.     The feature is marked as "semi-obsolete" but not "scheduled for removal"     since it's a plumbing command, scripts might use it, and Git testsuite     already uses it to test the state of the index. Marking it as obsolete because it was easily misunderstood, which I think was primarily due to documentation problems, is one strategy, but I think fixing the documentation is a better option. Especially since in the intervening time, "git ls-files -t" has become heavily used by sparse-checkout users where the same confusion just doesn't apply. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>