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.

- rm all files under storage/spider/hs_client/ except hs_compat.h
- rm storage/spider/spd_db_handlersocket.*
- unifdef -UHS_HAS_SQLCOM -UHAVE_HANDLERSOCKET \
  -m storage/spider/spd_* storage/spider/ha_spider.* storage/spider/hs_client/*
- remove relevant files from storage/spider/CMakeLists.txt

storage/spider/spd_db_mysql.h

@@ -560,54 +560,6 @@ public:
     uint binlog_pos_length,
     SPIDER_DB_RESULT **res
   );
-#if defined(HS_HAS_SQLCOM) && defined(HAVE_HANDLERSOCKET)
-  int append_sql(
-    char *sql,
-    ulong sql_length,
-    st_spider_db_request_key *request_key
-  );
-  int append_open_handler(
-    uint handler_id,
-    const char *db_name,
-    const char *table_name,
-    const char *index_name,
-    const char *sql,
-    st_spider_db_request_key *request_key
-  );
-  int append_select(
-    uint handler_id,
-    spider_string *sql,
-    SPIDER_DB_HS_STRING_REF_BUFFER *keys,
-    int limit,
-    int skip,
-    st_spider_db_request_key *request_key
-  );
-  int append_insert(
-    uint handler_id,
-    SPIDER_DB_HS_STRING_REF_BUFFER *upds,
-    st_spider_db_request_key *request_key
-  );
-  int append_update(
-    uint handler_id,
-    spider_string *sql,
-    SPIDER_DB_HS_STRING_REF_BUFFER *keys,
-    SPIDER_DB_HS_STRING_REF_BUFFER *upds,
-    int limit,
-    int skip,
-    bool increment,
-    bool decrement,
-    st_spider_db_request_key *request_key
-  );
-  int append_delete(
-    uint handler_id,
-    spider_string *sql,
-    SPIDER_DB_HS_STRING_REF_BUFFER *keys,
-    int limit,
-    int skip,
-    st_spider_db_request_key *request_key
-  );
-  void reset_request_queue();
-#endif
   size_t escape_string(
     char *to,
     const char *from,
@@ -798,9 +750,6 @@ protected:
   spider_string           *exec_ha_sql;
   bool                    reading_from_bulk_tmp_table;
   bool                    filled_up;
-#if defined(HS_HAS_SQLCOM) && defined(HAVE_HANDLERSOCKET)
-  SPIDER_DB_HS_STRING_REF_BUFFER hs_upds;
-#endif
   SPIDER_INT_HLD          *union_table_name_pos_first;
   SPIDER_INT_HLD          *union_table_name_pos_current;
 public:
@@ -907,14 +856,6 @@ public:
   int append_delete(
     spider_string *str
   );
-  #if defined(HS_HAS_SQLCOM) && defined(HAVE_HANDLERSOCKET)
-  #ifdef HANDLER_HAS_DIRECT_UPDATE_ROWS
-  int append_increment_update_set_part();
-  int append_increment_update_set(
-    spider_string *str
-  );
-  #endif
-  #endif
   int append_update_set_part();
   int append_update_set(
     spider_string *str
@@ -1445,23 +1386,6 @@ public:
   int reset_sql(
     ulong sql_type
   );
-#if defined(HS_HAS_SQLCOM) && defined(HAVE_HANDLERSOCKET)
-  int reset_keys(
-    ulong sql_type
-  );
-  int reset_upds(
-    ulong sql_type
-  );
-  int reset_strs(
-    ulong sql_type
-  );
-  int reset_strs_pos(
-    ulong sql_type
-  );
-  int push_back_upds(
-    SPIDER_HS_STRING_REF &info
-  );
-#endif
 #ifdef SPIDER_HAS_GROUP_BY_HANDLER
   int set_sql_for_exec(
     ulong sql_type,