[spl-record] Remove Data type from RecordData type

[samkim-crypto]

Problem

The record program uses the struct RecordData to represent record data in accounts.

pub struct RecordData {
    pub version: u8,
    pub authority: Pubkey,
    pub data: Data,
}

The Data type is an array of fixed size 8. It seems like this struct was added just for initial testing. The logic to support arbitrary length record data already exists in the processor logic.

By removing Data from the RecordData type and using it just as a header for data, we should be able to support arbitrary length record data.

Summary of changes

Removed the Data struct from state and updated the record program to support arbitrary length data.

This is a follow-up to #6054 (comment).

[joncinque]

Perfect, thanks for improving this!