fix explanations because it's used in other commands too.

Author: otegami

include/groonga/cache.h

@@ -96,16 +96,13 @@ grn_cache_close(grn_ctx *ctx, grn_cache *cache);
 GRN_API grn_rc
 grn_cache_current_set(grn_ctx *ctx, grn_cache *cache);
 /**
- * \brief Retrieve the current \ref grn_cache object used in the select command.
- *
- * \see For more details about the select command, please see
- *      https://groonga.org/docs/reference/commands/select.html.
+ * \brief Retrieve the current \ref grn_cache object.
  *
  * \param ctx The context object.
  *
- * \return The \ref grn_cache object is associated with the database in the
- *         select command context. If there is no specific cache, it returns
- *         the current cache which might be `NULL`.
+ * \return The \ref grn_cache object is associated with the database that the
+ *         context is using. If there is no specific cache, it returns the
+ *         current cache which might be NULL.
  */
 GRN_API grn_cache *
 grn_cache_current_get(grn_ctx *ctx);