Fix path to README.md file for app_service

Remove // from path for README.md since it's not searchable and
README.md file path is components/services/app_service/README.md
in code search.

Change-Id: I2ac9033a5584b4d75d841996606b58d102988547
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2453255
Auto-Submit: Oleh Lamzin <lamzin@google.com>
Reviewed-by: Nancy Wang <nancylingwang@chromium.org>
Commit-Queue: Oleh Lamzin <lamzin@google.com>
Cr-Commit-Position: refs/heads/master@{#814645}

chrome/browser/apps/app_service/README.md

 This is the browser-specific part of the App Service.
 
-See `//components/services/app_service/README.md`.
+See `components/services/app_service/README.md`.

components/services/app_service/public/cpp/app_registry_cache.h

@@ -31,7 +31,7 @@ namespace apps {
 //
 // This class is not thread-safe.
 //
-// See //components/services/app_service/README.md for more details.
+// See components/services/app_service/README.md for more details.
 class COMPONENT_EXPORT(APP_UPDATE) AppRegistryCache {
  public:
   class COMPONENT_EXPORT(APP_UPDATE) Observer : public base::CheckedObserver {

components/services/app_service/public/cpp/app_update.h

@@ -42,7 +42,7 @@ namespace apps {
 // are const. The constructor caller must guarantee that the AppPtr references
 // remain valid for the lifetime of the AppUpdate.
 //
-// See //components/services/app_service/README.md for more details.
+// See components/services/app_service/README.md for more details.
 class COMPONENT_EXPORT(APP_UPDATE) AppUpdate {
  public:
   // Modifies |state| by copying over all of |delta|'s known fields: those