Pass buf_block_t* to more functions that write redo log.

page_zip_write_node_ptr(), page_zip_write_blob_ptr(),
page_zip_compress_write_log_no_data():
Take buf_block_t* as parameter, and do not tolerate mtr=NULL.

page_zip_compress(): Do not tolerate mtr=NULL.

page_zip_dir_insert(): Take page_cur_t* as parameter.

mlog_write_initial_log_record(): Remove. This function was unused.

RecIterator::remove(): Remove the redundant page_zip parameter.

PageConverter::m_page_zip_ptr: Remove.