go/types: remove _ imports that are not needed anymore

Change-Id: I392b0a0083d6bea80a65f9eef46dd06b02a70e1b
Reviewed-on: https://go-review.googlesource.com/10082Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/types/eval_test.go

@@ -14,7 +14,6 @@ import (
 	"strings"
 	"testing"
 
-	_ "go/internal/gcimporter"
 	. "go/types"
 )
 

src/go/types/self_test.go

@@ -15,7 +15,6 @@ import (
 	"testing"
 	"time"
 
-	_ "go/internal/gcimporter"
 	. "go/types"
 )