[piexwasm] BUILD.gn: piex_loader.js has no external dependencies

After CL:2432150 piex_loader.js no longer depends on files app types
(external types). It only depends on DOM platform types.

js_library("piex_loader"):
  Remove deps=[]. Replace with a note about not adding any more deps
  so that piex_loader.js can be used standalone.

js_library("image_loader_util"):
  image_loader_util does not depend on piex_loader; remove that dep.

Bug: 1132695
Change-Id: I8df346343c86d68d610c72b2f77164153a800074
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435031Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811446}

ui/file_manager/image_loader/BUILD.gn

@@ -57,7 +57,6 @@ js_unittest("image_loader_unittest") {
 js_library("image_loader_util") {
   deps = [
     ":load_image_request",
-    ":piex_loader",
     "//ui/webui/resources/js:assert",
   ]
 }
@@ -89,10 +88,9 @@ js_unittest("image_loader_client_unittest") {
 }
 
 js_library("piex_loader") {
-  deps = [
-    ":load_image_request",
-    "//ui/file_manager/file_manager/foreground/js/metadata:image_orientation",
-  ]
+  # No dependencies should be added here, so the module can be loaded as a
+  # standalone .js file.
+
   externs_list = [ "//ui/file_manager/externs/platform.js" ]
 }