pw_span: Provide <span> through pw_polyfill

- Have pw_polyfill:overrides depend on pw_span.
- Remove explicit deps on pw_span.

Change-Id: Ibdd996d2764e737e487de5038cc84bd0f825c882
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/30043
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
diff --git a/docs/style_guide.rst b/docs/style_guide.rst
index b31a2eb..1087c51 100644
--- a/docs/style_guide.rst
+++ b/docs/style_guide.rst
@@ -577,10 +577,7 @@
 
   source_set("pw_sample_module") {
     public_configs = [ ":default_config" ]
-    public_deps = [
-      dir_pw_span,
-      dir_pw_status,
-    ]
+    public_deps = [ dir_pw_status ]
     public = [ "public/pw_sample_module/sample_module.h" ]
     sources = [
       "public/pw_sample_module/internal/sample_module.h",