Revert "Make Qt::Gui as a required module"

This reverts commit 9848b60e68.

Reason for revert: QTBUG-123489's root cause might not be here. The log shows Qt6Gui exists but build tools cannot find it. It will be fixed with another patch.

Pick-to: 6.7 6.6 6.5
Task-number: QTBUG-123489
Fixes: QTBUG-124304
Change-Id: I3313bdcb971bd480c92b3f0946610b4130396c58
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>

CMakeLists.txt

@@ -25,11 +25,11 @@ endif()
 
 find_package(Qt6 ${PROJECT_VERSION} CONFIG REQUIRED COMPONENTS
     Core
-    Gui
 )
 
 find_package(Qt6 ${PROJECT_VERSION} QUIET CONFIG OPTIONAL_COMPONENTS
     DBus
+    Gui
     OpenGL
     Quick
     Svg
@@ -42,4 +42,8 @@ find_package(Qt6 ${PROJECT_VERSION} QUIET CONFIG OPTIONAL_COMPONENTS
 #    return()
 #endif()
 # special case end
+if(NOT TARGET Qt::Gui)
+    message(NOTICE "Skipping the build as the condition \"TARGET Qt::Gui\" is not met.")
+    return()
+endif()
 qt_build_repo()