[shotwell] build: Drop broken reference to MaybeHeaderbarDialog.vala

[Rico Tzschichholz <ricotz src gnome org>]

commit 70cab367c581563b9e6bfd2bb4b8850fe78a8005
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sun Dec 24 09:25:30 2017 +0100

    build: Drop broken reference to MaybeHeaderbarDialog.vala

 shotwell.am |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)
---
diff --git a/shotwell.am b/shotwell.am
index 8b1479d..ec6cf0d 100644
--- a/shotwell.am
+++ b/shotwell.am
@@ -72,7 +72,6 @@ shotwell_SOURCES = \
        src/dialogs/SetBackground.vala \
        src/dialogs/ProgressDialog.vala \
        src/dialogs/SetBackgroundSlideshow.vala \
-       src/dialogs/MaybeHeaderbarDialog.vala \
        src/editing_tools/EditingTools.vala \
        src/editing_tools/RGBHistogramManipulator.vala \
        src/editing_tools/StraightenTool.vala \