remove awkward go.mod prepare

[gregwebs]

Feature Request

The go.mod prepare step in this Makefile of this project can make it confusing to add a new dependency.

I am hoping this was added due to issues with older go versions and it can be removed now?

[kennytm]

@gregwebs unfortunately as long as there is a cyclic dependency between BR and TiDB we can't avoid the go.mod1 trick 😢 (#554).

[gregwebs]

Okay, then the solution is to break the cycle. I am not familiar enough with Go modules to know if this necessitates multiple go.mod files in a single repo. But probably the core tidb code can be exposed as a library and kept separate from the in-process backup.

Keeping this issue open may help someone else who comes across this.