go/internal/gcimporter: rename file to better reflect new meaning

Also: Removed unused deref function.

Follow-up on https://golang.org/cl/143023.

Updates #27999.

Change-Id: I088265f0e3ce52029679407f0b84b734191d4d3c
Reviewed-on: https://go-review.googlesource.com/c/go/+/143024
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

src/go/internal/gcimporter/gcimporter.go

@@ -168,13 +168,6 @@ func Import(fset *token.FileSet, packages map[string]*types.Package, path, srcDi
 	return
 }
 
-func deref(typ types.Type) types.Type {
-	if p, _ := typ.(*types.Pointer); p != nil {
-		return p.Elem()
-	}
-	return typ
-}
-
 type byPath []*types.Package
 
 func (a byPath) Len() int           { return len(a) }

src/go/internal/gcimporter/support.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// This file implements support functionality for iimport.go.
+
 package gcimporter
 
 import (