cmd/internal/ld: delete Biobuf

Update #10652

This proposal deletes cmd/internal/ld.Biobuf and replaces all uses with
cmd/internal/obj.Biobuf. As cmd/internal/ld already imported cmd/internal/obj
there are no additional dependencies created.

Notes:

- ld.Boffset included more checks, so it was merged into obj.Boffset
- obj.Bflush was removed in 8d16253c90ae, so replaced all calls to
  ld.Bflush, with obj.Biobuf.Flush.
- Almost all of this change was prepared with sed.

Change-Id: I814854d52f5729a5a40c523c8188e465246b88da
Reviewed-on: https://go-review.googlesource.com/9660
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Dave Cheney <dave@cheney.net>
diff --git a/src/cmd/internal/ld/link.go b/src/cmd/internal/ld/link.go
index a92ab59..52390e7 100644
--- a/src/cmd/internal/ld/link.go
+++ b/src/cmd/internal/ld/link.go
@@ -30,7 +30,10 @@
 
 package ld
 
-import "encoding/binary"
+import (
+	"cmd/internal/obj"
+	"encoding/binary"
+)
 
 type LSym struct {
 	Name        string
@@ -106,7 +109,7 @@
 	Arch      *LinkArch
 	Debugasm  int32
 	Debugvlog int32
-	Bso       *Biobuf
+	Bso       *obj.Biobuf
 	Windows   int32
 	Goroot    string
 	Hash      map[symVer]*LSym