[pitivi] help: Remove obsolete welcome dialog info

[Alexandru Băluț <alexbalut src gnome org>]

commit 4ffb920f0e3c0ff68358d532385dace392589d08
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Wed Sep 11 03:11:13 2019 +0200

    help: Remove obsolete welcome dialog info

 help/C/welcomedialog.page | 41 -----------------------------------------
 help/meson.build          |  1 -
 2 files changed, 42 deletions(-)
---
diff --git a/help/meson.build b/help/meson.build
index e82d5586..ca7212c4 100644
--- a/help/meson.build
+++ b/help/meson.build
@@ -23,7 +23,6 @@ sources = [
     'trimming.page',
     'usingclips.page',
     'usingeffects.page',
-    'welcomedialog.page',
     'workwithprojects.page'
 ]