tour: drop deprecated build tag

[alexbozhenko]

drop deprecated +build syntax for tags
https://stackoverflow.com/a/68361186/1572363
https://pkg.go.dev/cmd/go#hdr-Build_constraints
https://go.dev/doc/go1.18#go-build-lines

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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