compiler: code cleanup (unused header file)

Remove inclusion of simple-ojbject.h (no longer needed);
    adjust comments.
    
    Reviewed-on: https://go-review.googlesource.com/28856

From-SVN: r240067

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-c2bd848dce774e8009ae1d8ee5d91ddc601ce37f
+6e791d2f3c183d55fdcabe3df20f01c029fd6d54
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/import.cc

@@ -7,7 +7,6 @@
 #include "go-system.h"
 
 #include "filenames.h"
-#include "simple-object.h"
 
 #include "go-c.h"
 #include "gogo.h"
@@ -233,7 +232,7 @@ Import::find_export_data(const std::string& filename, int fd, Location location)
   return NULL;
 }
 
-// Look for export data in a simple_object.
+// Look for export data in an object file.
 
 Import::Stream*
 Import::find_object_export_data(const std::string& filename,