MDEV-26858 Spider: Remove dead code related to HandlerSocket

Remove the dead-code, in Spider, which is related to the Spider's
HandlerSocket support. The code has been disabled for a long time
and it is unlikely that the code will be enabled.

Author: nayuta-yanagisawa

storage/spider/CMakeLists.txt

@@ -17,10 +17,7 @@ SET(SPIDER_SOURCES
   spd_param.cc spd_sys_table.cc spd_trx.cc spd_db_conn.cc spd_conn.cc
   spd_table.cc spd_direct_sql.cc spd_udf.cc spd_ping_table.cc
   spd_copy_tables.cc spd_i_s.cc spd_malloc.cc ha_spider.cc spd_udf.def
-  spd_db_mysql.cc spd_db_handlersocket.cc spd_db_oracle.cc
-  spd_group_by_handler.cc spd_db_include.cc
-  hs_client/config.cpp hs_client/escape.cpp hs_client/fatal.cpp
-  hs_client/hstcpcli.cpp hs_client/socket.cpp hs_client/string_util.cpp
+  spd_db_mysql.cc spd_db_oracle.cc spd_group_by_handler.cc spd_db_include.cc
 )
 
 IF(DEFINED ENV{ORACLE_HOME})