git-help -w: do not require to be in git repository

The users used to be able to say "git help cat-file" from anywhere, but
the browse-help script insisted to be in a git repository, which caused
"git help -w cat-file" to barf outside.  Correct it.

While at it, remove leftover debugging "echo".

Signed-off-by: Junio C Hamano <gitster@pobox.com>