[PATCH] Refactor: Extract XLogRecord info

Hi,

I refactored the code of extracting XLogRecord info.

In XLogRecord, the high 4 bits in xl_info is used by rmgr.

typedef struct XLogRecord
{
    uint32      xl_tot_len;     /* total len of entire record */
    TransactionId xl_xid;       /* xact id */
    XLogRecPtr  xl_prev;        /* ptr to previous record in log */
    uint8       xl_info;        /* flag bits, see below */
    RmgrId      xl_rmid;        /* resource manager for this record */
    /* 2 bytes of padding here, initialize to zero */
    pg_crc32c   xl_crc;         /* CRC for this record */

    /* XLogRecordBlockHeaders and XLogRecordDataHeader follow, no padding */

} XLogRecord;

I found lots of the code to get the info as below

XLogRecGetInfo(record) & ~XLR_INFO_MASK

Actually, we can directly use XLR_RMGR_INFO_MASK(0xF0)

instead of XLR_INFO_MASK(0x0F), which is easier to understand.
Remove XLR_INFO_MASK as it is not used any more.