sumdb/note: remove stray bytes.Buffer from Open
sumdb/note: remove stray bytes.Buffer from Open

This has been there from the beginning (CL 156324) without ever being
used.

Change-Id: I0cfb06ef1622315f84eb8ade525781e779012540
GitHub-Last-Rev: eb0423bad7d0998195a1730200a39f0fa1c49555
GitHub-Pull-Request: golang/mod#1
Reviewed-on: https://go-review.googlesource.com/c/mod/+/194639
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/mod,golang/mod