go/build: remove unused fileInfo.embedErr field

Change-Id: If86a0402dae32c57d07545ee6d818010e0e4b5ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/399255
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

Author: ianlancetaylor

src/go/build/build.go

@@ -1380,7 +1380,6 @@ type fileInfo struct {
 	parseErr error
 	imports  []fileImport
 	embeds   []fileEmbed
-	embedErr error
 }
 
 type fileImport struct {

src/go/build/read.go

@@ -390,7 +390,7 @@ func readComments(f io.Reader) ([]byte, error) {
 // readGoInfo expects a Go file as input and reads the file up to and including the import section.
 // It records what it learned in *info.
 // If info.fset is non-nil, readGoInfo parses the file and sets info.parsed, info.parseErr,
-// info.imports, info.embeds, and info.embedErr.
+// info.imports and info.embeds.
 //
 // It only returns an error if there are problems reading the file,
 // not for syntax errors in the file itself.