go/internal/gcimporter: remove support for binary export data

There should no longer be any clients of the binary export data format,
and it has been deleted from the standard library, so we can now delete
it from x/tools. This change deletes bimport.go, bexport.go, and
bexport_test.go, transferring any shared code to the corresponding
"i" files.

Fixes golang/go#37312

Change-Id: I25d8a36e89c33e10de68b586245722794c4d52c3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/229987
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: stamblerre

go/gcexportdata/gcexportdata.go

@@ -85,15 +85,11 @@ func Read(in io.Reader, fset *token.FileSet, imports map[string]*types.Package,
 		return gcimporter.ImportData(imports, path, path, bytes.NewReader(data))
 	}
 
-	// The indexed export format starts with an 'i'; the older
-	// binary export format starts with a 'c', 'd', or 'v'
-	// (from "version"). Select appropriate importer.
-	if len(data) > 0 && data[0] == 'i' {
-		_, pkg, err := gcimporter.IImportData(fset, imports, data[1:], path)
-		return pkg, err
+	// The indexed export format starts with an 'i'.
+	if len(data) == 0 || data[0] != 'i' {
+		return nil, fmt.Errorf("unknown export data format")
 	}
-
-	_, pkg, err := gcimporter.BImportData(fset, imports, data, path)
+	_, pkg, err := gcimporter.IImportData(fset, imports, data[1:], path)
 	return pkg, err
 }