osd: don't build unnecessary parts of SnapMapper for crimson

This commits skips building two call-sites of `omap_get_iterator()`
of `ObjectStore` which are bypassing the `OSDriver` abstraction
layer.

1. `SnapMapper::convert_legacy()` likely never be needed by
crimson and we can leave it unchanged.

2. `SnapMapper::Subber` isn't needed right now but will be
needed in the future.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

src/osd/SnapMapper.cc

@@ -657,6 +657,7 @@ void SnapMapper::record_purged_snaps(
 }
 
 
+#ifndef WITH_SEASTAR
 bool SnapMapper::Scrubber::_parse_p()
 {
   if (!psit->valid()) {
@@ -760,6 +761,7 @@ void SnapMapper::Scrubber::run()
   psit = ObjectMap::ObjectMapIterator();
   mapit = ObjectMap::ObjectMapIterator();
 }
+#endif // !WITH_SEASTAR
 
 
 // -------------------------------------
@@ -816,6 +818,7 @@ std::string SnapMapper::convert_legacy_key(
     + "_" + object_suffix;
 }
 
+#ifndef WITH_SEASTAR
 int SnapMapper::convert_legacy(
   CephContext *cct,
   ObjectStore *store,
@@ -874,3 +877,4 @@ int SnapMapper::convert_legacy(
   }
   return 0;
 }
+#endif // !WITH_SEASTAR

src/osd/SnapMapper.h

@@ -141,6 +141,7 @@ public:
   static const char *PURGED_SNAP_EPOCH_PREFIX;
   static const char *PURGED_SNAP_PREFIX;
 
+#ifndef WITH_SEASTAR
   struct Scrubber {
     CephContext *cct;
     ObjectStore *store;
@@ -187,6 +188,7 @@ public:
     ObjectStore::CollectionHandle& ch,
     ghobject_t hoid,
     unsigned max);
+#endif
 
   static void record_purged_snaps(
     CephContext *cct,