complete: zsh: trivial simplification

complete: zsh: trivial simplification

There should be no functional changes.

The only reason I wrapped this code around a sub-function is because zsh
did the same in it's bashcompinit script in order to declare the special
variable 'words' as hidden, but only in this context.

There's no need for that any more since we access __git_main directly,
so 'words' is not modified, so there's no need for the sub-function.

In zsh mode the array indexes are different though.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>