crimson/so/seastore: clean up logical_child_node.cc

logical_child_node.cc is totally duplicated with lba_mapping.cc and
should be removed

Signed-off-by: Xuehan Xu <[email protected]>

Author: xxhdx1985126

src/crimson/os/seastore/CMakeLists.txt

@@ -1,7 +1,6 @@
 set(crimson_seastore_srcs
   cached_extent.cc
   lba_mapping.cc
-  logical_child_node.cc
   seastore_types.cc
   segment_manager.cc
   segment_manager/ephemeral.cc