Revert "weston.ini: Use 'modeline' key for modeline example"

This reverts commit 97a56145636316fdb431b91ec64adff217287cd9.

The current code detects the mode key, not modeline. Reference:
http://cgit.freedesktop.org/wayland/weston/tree/src/compositor-drm.c#n2464
diff --git a/weston.ini b/weston.ini
index 431bfa9..c6cff76 100644
--- a/weston.ini
+++ b/weston.ini
@@ -48,7 +48,7 @@
 
 #[output]
 #name=VGA1
-#modeline=173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync
+#mode=173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync
 #transform=flipped
 
 #[output]