Refactor: remoted: Use g_strchug() in load_env_vars()

Skipping (or now, stripping) leading whitespace is one fewer thing we
have to do ourselves. g_strchug() is defined to operate on a (gchar *),
but it modifies its argument in place without
allocating/rellocating/freeing memory, so it's safe.

Since find_env_var_name() only needs to return one pointer now, it
doesn't need output arguments.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>