WL#9219: Remove cross compatibility code for binlog V1-V3

Affects: Server-8.0   —   Status: Complete

There are several versions of the binary log file format:
v1: Used in MySQL 3.23
v3: Used in MySQL 4.0.2 through 4.1
v4: Used in MySQL 5.0 and up
A v2 format was used briefly (in early MySQL 4.0.x versions),
but it is obsolete and no longer supported.

To support replication between different versions, there are some compatibility
code for converting old binlog format to new binlog format. According to the
support policy, v1 and v3 are out of the support period.

To make the code simple and readable, this worklog will remove the
compatibility code between binlog versions. And replication will just
support binlog v4 since this worklog.