remove data block type in wal file

[bartliu827]

Describe the issue
There is only on block type in wal data block,Do we need to keep it?

What you like us to do

Additional context
Add any other context about the issue here.

[zipper-meng]

Removed type wal::Block and adjusted dependents.

/// Before
pub struct WalRecordData {
     pub typ: WalType,
     pub seq: u64,
     pub block: Block,
 }
/// After
pub struct WalRecordData {
     pub typ: WalType,
     pub seq: u64,
     pub block: Option<wal_store::RaftEntry>,
 }