builder/remotecontext/gitutils: switch back to os/exec
builder/remotecontext/gitutils: switch back to os/exec

This is a partial revert of 7ca0cb7ffafc5339ac5fa575ce3f8b479c3643bf, which
switched from os/exec to the golang.org/x/sys/execabs package to mitigate
security issues (mainly on Windows) with lookups resolving to binaries in the
current directory.

from the go1.19 release notes https://go.dev/doc/go1.19#os-exec-path

> ## PATH lookups
>
> Command and LookPath no longer allow results from a PATH search to be found
> relative to the current directory. This removes a common source of security
> problems but may also break existing programs that depend on using, say,
> exec.Command("prog") to run a binary named prog (or, on Windows, prog.exe) in
> the current directory. See the os/exec package documentation for information
> about how best to update such programs.
>
> On Windows, Command and LookPath now respect the NoDefaultCurrentDirectoryInExePath
> environment variable, making it possible to disable the default implicit search
> of “.” in PATH lookups on Windows systems.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

moby/moby,mahak/docker,thaJeztah/docker,thaJeztah/docker,trebonian/docker,thaJeztah/docker,moby/moby,trebonian/docker,jimjag/docker,mahak/docker,moby/moby,thaJeztah/docker,konstruktoid/docker-upstream,konstruktoid/docker-upstream,Ramzec/docker,konstruktoid/docker-upstream,mahak/docker,Ramzec/docker,trebonian/docker,Ramzec/docker,mahak/docker,jimjag/docker,trebonian/docker,konstruktoid/docker-upstream,jimjag/docker,jimjag/docker,moby/moby,Ramzec/docker