Revert "Use std::function instead of base::function_ref"

Revert submission 2780893

Reason for revert: breaking boot tests

Bug: 308214260

Reverted changes: /q/submissionid:2780893

Change-Id: Ibbd9bf2c9eb1389c9b8217cc75a98a3ec13b77d8
diff --git a/libs/binder/RpcState.h b/libs/binder/RpcState.h
index 2a954e6..1fe71a5 100644
--- a/libs/binder/RpcState.h
+++ b/libs/binder/RpcState.h
@@ -16,7 +16,6 @@
 #pragma once
 
 #include <android-base/unique_fd.h>
-#include <binder/Functional.h>
 #include <binder/IBinder.h>
 #include <binder/Parcel.h>
 #include <binder/RpcSession.h>
@@ -191,7 +190,7 @@
     [[nodiscard]] status_t rpcSend(
             const sp<RpcSession::RpcConnection>& connection, const sp<RpcSession>& session,
             const char* what, iovec* iovs, int niovs,
-            const std::optional<binder::impl::SmallFunction<status_t()>>& altPoll,
+            const std::optional<android::base::function_ref<status_t()>>& altPoll,
             const std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds =
                     nullptr);
     [[nodiscard]] status_t rpcRec(