sstable_directory: Move sstable_directory::pending_delete_result

... to where it belongs -- to the filesystem storage driver itself.
Continuation of the previous patch.

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

sstables/sstable_directory.hh

@@ -291,11 +291,6 @@ public:
     using can_be_remote = bool_class<struct can_be_remote_tag>;
     future<> collect_output_unshared_sstables(std::vector<sstables::shared_sstable> resharded_sstables, can_be_remote);
 
-    struct pending_delete_result {
-        sstring pending_delete_log;
-        std::unordered_set<sstring> prefixes;
-    };
-
     // When we compact sstables, we have to atomically instantiate the new
     // sstable and delete the old ones.  Otherwise, if we compact A+B into C,
     // and if A contained some data that was tombstoned by B, and if B was

sstables/storage.cc

@@ -480,7 +480,7 @@ future<> filesystem_storage::wipe(const sstable& sst, sync_dir sync) noexcept {
 }
 
 future<atomic_delete_context> filesystem_storage::atomic_delete_prepare(const std::vector<shared_sstable>& ssts) const {
-    sstable_directory::pending_delete_result res;
+    atomic_delete_context res;
 
     for (const auto& sst : ssts) {
         auto prefix = sst->_storage->prefix();

sstables/storage.hh

@@ -23,7 +23,6 @@
 #include "sstables/component_type.hh"
 #include "sstables/generation_type.hh"
 #include "utils/disk-error-handler.hh"
-#include "sstables/sstable_directory.hh"
 
 class schema;
 
@@ -41,7 +40,10 @@ class sstable;
 class sstables_manager;
 class entry_descriptor;
 
-using atomic_delete_context = sstable_directory::pending_delete_result;
+struct atomic_delete_context {
+    sstring pending_delete_log;
+    std::unordered_set<sstring> prefixes;
+};
 
 class opened_directory final {
     std::filesystem::path _pathname;