[!gofumpt] skip 'don''t add or remove imports'

gofumpt -w foo.go
cmp foo.go foo.go.golden

gofumpt -d foo.go.golden
! stdout .

-- foo.go --
package p

import "C"
import "os"

import "C"
import (
	"io"
	"utf8"
)

-- foo.go.golden --
package p

import "C"
import "os"

import "C"
import (
	"io"
	"utf8"
)