submodule: stop sanitizing config options

The point of having a whitelist of command-line config
options to pass to submodules was two-fold:

  1. It prevented obvious nonsense like using core.worktree
     for multiple repos.

  2. It could prevent surprise when the user did not mean
     for the options to leak to the submodules (e.g.,
     http.sslverify=false).

For case 1, the answer is mostly "if it hurts, don't do
that". For case 2, we can note that any such example has a
matching inverted surprise (e.g., a user who meant
http.sslverify=true to apply everywhere, but it didn't).

So this whitelist is probably not giving us any benefit, and
is already creating a hassle as people propose things to put
on it. Let's just drop it entirely.

Note that we still need to keep a special code path for
"prepare the submodule environment", because we still have
to take care to pass through $GIT_CONFIG_PARAMETERS (and
block the rest of the repo-specific environment variables).

We can do this easily from within the submodule shell
script, which lets us drop the submodule--helper option
entirely (and it's OK to do so because as a "--" program, it
is entirely a private implementation detail).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule.h

@@ -43,19 +43,10 @@ int find_unpushed_submodules(unsigned char new_sha1[20], const char *remotes_nam
 int push_unpushed_submodules(unsigned char new_sha1[20], const char *remotes_name);
 void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
 
-/*
- * This function is intended as a callback for use with
- * git_config_from_parameters(). It ignores any config options which
- * are not suitable for passing along to a submodule, and accumulates the rest
- * in "data", which must be a pointer to a strbuf. The end result can
- * be put into $GIT_CONFIG_PARAMETERS for passing to a sub-process.
- */
-int sanitize_submodule_config(const char *var, const char *value, void *data);
-
 /*
  * Prepare the "env_array" parameter of a "struct child_process" for executing
  * a submodule by clearing any repo-specific envirionment variables, but
- * retaining any config approved by sanitize_submodule_config().
+ * retaining any config in the environment.
  */
 void prepare_submodule_repo_env(struct argv_array *out);