fix: default map is the runnable DemoMap, not the engine template

A plain packaged launch (./GigLine.sh with no -map) opened
/Engine/Maps/Templates/OpenWorld — an empty engine template with nothing to
do, which presented as a 'stuck' window with no working mouse/keys. The
GameDefaultMap setting lived in DefaultGame.ini and wasn't taking effect.

Move GameMapsSettings (GameDefaultMap/EditorStartupMap/ServerDefaultMap/
TransitionMap = /Game/Hollywood/DemoMap) into DefaultEngine.ini alongside the
GlobalDefaultGameMode, and drop the stale ReviewMap default from DefaultGame.ini.
Verified: plain ./GigLine.sh now loads /Game/Hollywood/DemoMap, Enhanced Input
initializes, Vulkan window opens.

Game/GigLine/Config/DefaultGame.ini

@@ -17,8 +17,4 @@ UsePakFile=True
 +DirectoriesToAlwaysCook=/Game/Hollywood
 +DirectoriesToAlwaysCook=/Game/Test
 
-[/Script/EngineSettings.GameMapsSettings]
-; Temporary default while the demo map is being built; GameMapsSettings in
-; DefaultEngine.ini still names the game mode only.
-GameDefaultMap=/Game/Test/ReviewMap
-EditorStartupMap=/Game/Test/ReviewMap
+