submodule: remove extra line feeds between callback struct and macro

submodule: remove extra line feeds between callback struct and macro

Many `submodule--helper` subcommands follow the convention that a struct
defines their callback data, and the declaration of that struct is
followed immediately by a macro to use in static initializers, without
any separating empty line.

Let's align the `init`, `status` and `sync` subcommands with that convention.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Helped-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Shourya Shukla <shouryashukla.oo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>