Remove redundant build tags

[alexandear]

This PR removes outdated in Go 1.21 // +build comments by running the command:

go fix -fix buildtag ./...

From https://pkg.go.dev/cmd/[email protected]#hdr-Build_constraints:

Go versions 1.16 and earlier used a different syntax for build constraints, with a "// +build" prefix. The gofmt command will add an equivalent //go:build constraint when encountering the older syntax.

As the file name ends with _linux.go or _windows.go, we don't need //go:build linux and //go:build windows according to the documentation.