env: Drop common init() functions

Most of the init() implementations just use the default environment.
Adjust env_init_new() to do this automatically, and drop the redundant
code.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/environment.h b/include/environment.h
index ff3f542..7eaba72 100644
--- a/include/environment.h
+++ b/include/environment.h
@@ -259,7 +259,8 @@
 	 *
 	 * This method is optional.
 	 *
-	 * @return 0 if OK, -ve on error
+	 * @return 0 if OK, -ENOENT if no initial environment could be found,
+	 * other -ve on error
 	 */
 	int (*init)(void);
 };