The `go` directive inside go.mod determines certain behaviors of
the go command. Since we're using go 1.17 everywhere, we should
update our module's go directive to reflect that, and update its contents
to match the new behavior.
Particularly, updating to 1.17 here means that all indirect dependencies
are listed directly inside go.mod (in a separate block, to keep things clean),
and the go.sum and go.mod files are deleted from vendored dependencies
so that the go tool can correctly find the root of the module even when run
from a vendored dependency's subdirectory.
This is a sort of proof of concept of the Redis interaction, which will
evolve into a tool for inspection and manual repair of missing entries,
if we find ourselves needing to do that.
The important bits here are rocsp/rocsp.go and
cmd/rocsp-tool/main.go. Also, the newly-vendored Redis client.