all: remove obsolete build tags

[alexandear]

This PR removes all // +build comments because they have been obsolete since Go 1.17. From the doc:

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.

[aarzilli]

What's the minimum version that we still actually build with?

[alexandear]

The minimum supported version is Go 1.17 as stated in the go.mod.

I got errors when building with Go 1.16:

# golang.org/x/sys/unix
vendor/golang.org/x/sys/unix/syscall.go:83:16: undefined: unsafe.Slice
vendor/golang.org/x/sys/unix/syscall_bsd.go:248:20: undefined: unsafe.Slice
vendor/golang.org/x/sys/unix/syscall_darwin.go:94:8: undefined: unsafe.Slice
vendor/golang.org/x/sys/unix/syscall_unix.go:118:7: undefined: unsafe.Slice
vendor/golang.org/x/sys/unix/sysvshm_unix.go:33:7: undefined: unsafe.Slice
make: *** [build] Error 1

[aarzilli]

Ah yes, it's because of the cilium update to fix the bug. Ok, LGTM, but we wanted to freeze for a week before releasing 1.21.1, so it will have to wait.

[derekparker]

LGTM