pw_span: Switch from pw::span to std::span

Replace pw::span with std::span and "pw_span/span.h" with <span>
throughout the codebase.

Change-Id: Ib1fa873168b6093794e861611d750fcad6285d6c
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/12801
Commit-Queue: Wyatt Hepler <hepler@google.com>
Reviewed-by: Rob Mohr <mohrr@google.com>
Reviewed-by: Keir Mierle <keir@google.com>

pw_rpc/server_test.cc

diff --git a/pw_rpc/server_test.cc b/pw_rpc/server_test.cc
index 6b5905d..7082772 100644
--- a/pw_rpc/server_test.cc
+++ b/pw_rpc/server_test.cc
@@ -76,15 +76,16 @@
   Server server_;
   TestService service_;
 
-  span<const byte> EncodeRequest(PacketType type,
-                                 uint32_t channel_id,
-                                 uint32_t service_id,
-                                 uint32_t method_id,
-                                 span<const byte> payload = kDefaultPayload) {
+  std::span<const byte> EncodeRequest(
+      PacketType type,
+      uint32_t channel_id,
+      uint32_t service_id,
+      uint32_t method_id,
+      std::span<const byte> payload = kDefaultPayload) {
     auto sws = Packet(type, channel_id, service_id, method_id, payload)
                    .Encode(request_buffer_);
     EXPECT_EQ(Status::OK, sws.status());
-    return span(request_buffer_, sws.size());
+    return std::span(request_buffer_, sws.size());
   }
 
  private: