cmd/go: simplify compiler import config preparation

I realized this simplification was possible when writing the vet loop
(just above the code being modified here) but never circled back
to make the compiler loop match.

Change-Id: Ic2277d2a4b6d94ea4897cc3615fc1a29f2fb243c
Reviewed-on: https://go-review.googlesource.com/78395
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/go/internal/load/pkg.go

@@ -406,9 +406,6 @@ func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPo
 		// Load package.
 		// Import always returns bp != nil, even if an error occurs,
 		// in order to return partial information.
-		//
-		// TODO: After Go 1, decide when to pass build.AllowBinary here.
-		// See issue 3268 for mistakes to avoid.
 		buildMode := build.ImportComment
 		if mode&UseVendor == 0 || path != origPath {
 			// Not vendoring, or we already found the vendored path.

src/cmd/go/internal/work/exec.go

@@ -502,23 +502,10 @@ func (b *Builder) build(a *Action) (err error) {
 
 	// Prepare Go import config.
 	var icfg bytes.Buffer
-	for _, a1 := range a.Deps {
-		p1 := a1.Package
-		if p1 == nil || p1.ImportPath == "" {
-			continue
-		}
-		path := p1.ImportPath
-		i := strings.LastIndex(path, "/vendor/")
-		if i >= 0 {
-			i += len("/vendor/")
-		} else if strings.HasPrefix(path, "vendor/") {
-			i = len("vendor/")
-		} else {
-			continue
-		}
-		fmt.Fprintf(&icfg, "importmap %s=%s\n", path[i:], path)
-		if vcfg != nil {
-			vcfg.ImportMap[path[i:]] = path
+	for i, raw := range a.Package.Internal.RawImports {
+		final := a.Package.Imports[i]
+		if final != raw {
+			fmt.Fprintf(&icfg, "importmap %s=%s\n", raw, final)
 		}
 	}