decklink-output-ui: Remove Qt5X11Extras

Qt5X11Extras (QX11Info) was added in
762983b5d853ba8444c4efee450ea872b294060e, but it doesn't seem to
actually be used. Qt6 doesn't yet ship X11Extras, so let's remove it.

UI/frontend-plugins/decklink-output-ui/CMakeLists.txt

@@ -9,8 +9,6 @@ if(UNIX AND NOT APPLE)
 	find_package(X11 REQUIRED)
 	link_libraries(${X11_LIBRARIES})
 	include_directories(${X11_INCLUDE_DIR})
-
-	find_package(Qt5X11Extras REQUIRED)
 endif()
 
 set(decklink-ouput-ui_HEADERS
@@ -69,11 +67,6 @@ target_link_libraries(decklink-ouput-ui
 	Qt5::Widgets
 	libobs)
 
-if(UNIX AND NOT APPLE)
-	target_link_libraries(decklink-ouput-ui
-		Qt5::X11Extras)
-endif()
-
 set_target_properties(decklink-ouput-ui PROPERTIES FOLDER "frontend")
 
 install_obs_plugin_with_data(decklink-ouput-ui data)