[pitivi] docs: Remove useless page

[Thibault Saunier <tsaunier src gnome org>]

commit cfe163d622a37632f5376df4b760d0a91ef980ff
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Wed Sep 12 04:04:48 2018 +0200

    docs: Remove useless page

 docs/design/UI_components.md | 7 -------
 docs/sitemap.txt             | 1 -
 2 files changed, 8 deletions(-)
---
diff --git a/docs/sitemap.txt b/docs/sitemap.txt
index e18eee23..505ac030 100644
--- a/docs/sitemap.txt
+++ b/docs/sitemap.txt
@@ -79,7 +79,6 @@ index.md
                design/Title_editor_design.md
                design/UI_Design_Variants.md
                design/UI_Implementation.md
-               design/UI_components.md
                design/Multi-Layer_Editing.md
        attic.md
                attic/GNonLin.md