git_push_config: drop cargo-culted wt_status pointer

git_push_config: drop cargo-culted wt_status pointer

The push config callback does not expect any incoming data
via the void pointer. And if it did, it would certainly not
be a "struct wt_status". This probably got picked up
accidentally in b945901 (push: heed user.signingkey for
signed pushes, 2014-10-22), which copied the template for
the config callback from builtin/commit.c.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>