git-p4: remove "debug" verb

git-p4: remove "debug" verb

The git-p4 "debug" verb is described as "A tool to debug the output of
p4 -G".

The verb is not documented in any detail, but implements a function
which executes an arbitrary p4 command with the -G flag, which causes
perforce to format all output as marshalled Python dictionary objects.

The verb was implemented early in the history of git-p4, and may once
have served a useful purpose to the authors in the early stages of
development. However, the "debug" verb is no longer being used by the
current developers (and users) of git-p4, and whatever purpose the verb
previously offered is easily replaced by invoking p4 directly.

This patch therefore removes the verb from git-p4.

Signed-off-by: Joel Holdsworth <jholdsworth@nvidia.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>