Remove top border on FilesMessage

The .dialog-header.files-ng which this component sits directly below
already has a bottom border and we don't want a double line.

Bug: 1099557
Change-Id: I808deb34484b80f984ec31b60424ede0b4ecc2f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2289171Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786567}

ui/file_manager/file_manager/foreground/elements/files_message.js

@@ -13,7 +13,6 @@ const filesMessageTemplate = `
     }
 
     :host {
-      border-top: 1px solid var(--google-grey-refresh-300);
       border-bottom: 1px solid var(--google-grey-refresh-300);
       color: var(--cr-primary-text-color);
       display: flex;