contrib: remove "remotes2config.sh"

Remotes can be configured either via a repository's config or by using
the ".git/branches/" or ".git/remotes/" directories. Back when the new
config-based mechanism has been introduced we also introduced a helper
script that migrates from the old-style remote configuration to the new
config-based mechanism.

With the recent removal announcement for the two directories we also
started to instruct users to migrate repositories that still use these
mechanism to use config-based remotes. Notably though, the migration
path doesn't even use the migration script. Instead, git-remote(1)
itself knows how to migrate any such remote via `git remote rename`.

In fact, a full migration _cannot_ use the script as it only knows to
migrate remotes from ".git/remotes/", but not ".git/branches/". As such,
the migration path via `git remote rename` is the only feasible way to
fully migrate repositories over to the new format.

Last but not least, the script doesn't even work as-is as it sources
"git-sh-setup". For this to work it would need to be invoked either via
Git so that this script is in our PATH, users would have to manually
call it with an adjusted PATH, or distributions need to install the
script into "$prefix/libexec/git-core" with a "git-" prefix. All of
these steps are unlikely enough to underpin the claim that this script
is not used at all.

So given that:

  - The script cannot perform a full migration of all deprecated remote
    types.

  - We don't advertise it anywhere.

  - It has been basically untouched since 2007.

  - It doesn't even work unless users do manual steps.

It should be safe enough to just remove it. Do so.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t