cmd/internal/obj: remove useless Trimpath field and fix users

http://golang.org/cl/7623 refactored how line history works and
introduced a new TrimPathPrefix field to replace the existing Trimpath
field, but never removed the latter or updated its users.

Fixes #10503.

Change-Id: Ief90a55b6cef2e8062b59856a4c7dcc0df01d3f2
Reviewed-on: https://go-review.googlesource.com/9113
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>

src/cmd/asm/main.go

@@ -40,7 +40,7 @@ func main() {
 	if *flags.PrintOut {
 		ctxt.Debugasm = 1
 	}
-	ctxt.Trimpath = *flags.TrimPath
+	ctxt.LineHist.TrimPathPrefix = *flags.TrimPath
 	ctxt.Flag_dynlink = *flags.Dynlink
 	if *flags.Shared || *flags.Dynlink {
 		ctxt.Flag_shared = 1

src/cmd/internal/asm/asm.go

@@ -192,7 +192,7 @@ func Main() {
 	flag.Var((*count)(&debug['S']), "S", "print assembly and machine code")
 	flag.Var((*count)(&debug['m']), "m", "debug preprocessor macros")
 	flag.StringVar(&outfile, "o", "", "file: set output file")
-	flag.StringVar(&Ctxt.Trimpath, "trimpath", "", "prefix: remove prefix from recorded source file paths")
+	flag.StringVar(&Ctxt.LineHist.TrimPathPrefix, "trimpath", "", "prefix: remove prefix from recorded source file paths")
 
 	flag.Parse()
 

src/cmd/internal/gc/lex.go

@@ -213,7 +213,7 @@ func Main() {
 	obj.Flagcount("r", "debug generated wrappers", &Debug['r'])
 	obj.Flagcount("race", "enable race detector", &flag_race)
 	obj.Flagcount("s", "warn about composite literals that can be simplified", &Debug['s'])
-	obj.Flagstr("trimpath", "prefix: remove prefix from recorded source file paths", &Ctxt.Trimpath)
+	obj.Flagstr("trimpath", "prefix: remove prefix from recorded source file paths", &Ctxt.LineHist.TrimPathPrefix)
 	obj.Flagcount("u", "reject unsafe code", &safemode)
 	obj.Flagcount("v", "increase debug verbosity", &Debug['v'])
 	obj.Flagcount("w", "debug type checking", &Debug['w'])

src/cmd/internal/obj/link.go

@@ -439,7 +439,6 @@ type Link struct {
 	Bso                *Biobuf
 	Pathname           string
 	Windows            int32
-	Trimpath           string
 	Goroot             string
 	Goroot_final       string
 	Enforce_data_order int32