Revert "cmd/utils: fix compilation issue on openbsd (#22511)"

[gballet]

#22511 presented an incorrect fix and it was merged in haste. I am working on the correct fix in the background.

[karalabe]

We were discussing that we should drop our custom disk space tracker altogether and just use gopsutils/disk. Doesn't make sense to reimplement something, especially if it's a pain to port.

[gballet]

agreed, the fix to gopsutil is in progress

[gballet]

btw the "fix" that was hastily merged didn't fix anything on master:

# github.com/shirou/gopsutil/mem
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:21:17: undefined: CTLVm
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:21:24: undefined: VmUvmexp
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:26:14: undefined: sizeOfUvmexp
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:29:13: undefined: Uvmexp
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:43:17: undefined: CTLVm
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:43:24: undefined: VmUvmexp
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:48:14: undefined: sizeOfUvmexp
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:51:13: undefined: Uvmexp
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:72:16: undefined: CTLVfs
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:72:24: undefined: VfsGeneric
../../../../pkg/mod/github.com/shirou/gopsutil@v2.20.5+incompatible/mem/mem_openbsd.go:72:24: too many errors

[holiman]

btw the "fix" that was hastily merged didn't fix anything on maste

Well, arguably it fixed an openbsd compilation error, but not all of them.