cmd/objdump: remove two unused types

The last mention of those types in this package are in:

  commit 6bd0d054
  Author: Russ Cox <rsc@golang.org>
  Date:   Thu Nov 6 19:56:55 2014 -0500

      cmd/objdump, cmd/pprof: factor disassembly into cmd/internal/objfile

Found with honnef.co/go/tools/cmd/unused.

Change-Id: Iacc2902f7d0784ac0efdd92da239f3e97491469a
Reviewed-on: https://go-review.googlesource.com/41472Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/objdump/main.go

@@ -53,9 +53,6 @@ func usage() {
 	os.Exit(2)
 }
 
-type lookupFunc func(addr uint64) (sym string, base uint64)
-type disasmFunc func(code []byte, pc uint64, lookup lookupFunc) (text string, size int)
-
 func main() {
 	log.SetFlags(0)
 	log.SetPrefix("objdump: ")