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/pw_cpu_exception/BUILD.gn b/pw_cpu_exception/BUILD.gn
index f2562e2..7c6f45d 100644
--- a/pw_cpu_exception/BUILD.gn
+++ b/pw_cpu_exception/BUILD.gn
@@ -61,10 +61,7 @@
 pw_facade("handler") {
   backend = pw_cpu_exception_HANDLER_BACKEND
   public_configs = [ ":default_config" ]
-  public_deps = [
-    "$dir_pw_preprocessor",
-    "$dir_pw_span",
-  ]
+  public_deps = [ "$dir_pw_preprocessor" ]
   sources = [ "start_exception_handler.cc" ]
   public = [ "public/pw_cpu_exception/handler.h" ]
 }
@@ -76,7 +73,6 @@
 pw_facade("support") {
   backend = pw_cpu_exception_SUPPORT_BACKEND
   public_configs = [ ":default_config" ]
-  public_deps = [ "$dir_pw_span" ]
   public = [ "public/pw_cpu_exception/support.h" ]
 }