mrec_ext_t: Introduce DELETE_ROW_FORMAT_REDUNDANT,
DELETE_ROW_FORMAT_DYNAMIC.

mtr_t::page_delete(): Write DELETE_ROW_FORMAT_REDUNDANT or
DELETE_ROW_FORMAT_DYNAMIC log records. We log the byte offset
of the preceding record, so that on recovery we can easily
find everything to update. For DELETE_ROW_FORMAT_DYNAMIC,
we must also write the header and data size of the record.

We will retain the physical logging for ROW_FORMAT=COMPRESSED pages.

page_zip_dir_balance_slot(): Renamed from page_dir_balance_slot(),
and specialized for ROW_FORMAT=COMPRESSED only.

page_rec_set_n_owned(), page_dir_slot_set_n_owned(),
page_dir_balance_slot(): New variants that do not write any log.

page_mem_free(): Take data_size, extra_size as parameters.
Always zerofill the record payload.

page_cur_delete_rec(): For other than ROW_FORMAT=COMPRESSED,
only write log by mtr_t::page_delete().