go.mod: remove replace directive for google.golang.org/protobuf

[tbg]

#104302 (comment) introduces a replace directive

replace google.golang.org/protobuf => google.golang.org/protobuf v1.29.1

In the meantime, our google protobuf version has been upgraded to v1.3.2 (though I don't know what motivated the last upgrade¹), and is likely to keep drifting ahead.

This problem is likely connected (in ways I am still understanding) to gogo/protobuf (which we use) and the grpc version, and contributes to friction in relation to these dependencies.

We should figure out what it would take to remove the above replace directive.

Jira issue: CRDB-44307

Footnotes

1. https://github.com/cockroachdb/cockroach/commit/614323229514f307e98029c1b0b1b8740889e2af#diff-33ef32bf6c23acb95f5902d7097b7a1d5128ca061167ec0716715b0b9eeaa5f6L68 ↩

[tbg]

#134943 seems to fix it - it builds locally, let's see what CI says.