HackStudio: Remove the visual form editor

Okay we've tried this twice now, and nobody ends up working on it.
Meanwhile, more and more people are using GML, and I think it's safe
to say that GML is the future of GUI development here.

So let's get rid of the old form editor from HackStudio and pave the
way for integrating GML editing into the IDE instead. :^)

Userland/DevTools/HackStudio/CMakeLists.txt

@@ -6,7 +6,6 @@ compile_gml(Dialogs/NewProjectDialog.gml Dialogs/NewProjectDialogGML.h new_proje
 set(SOURCES
     CodeDocument.cpp
     ClassViewWidget.cpp
-    CursorTool.cpp
     Debugger/BacktraceModel.cpp
     Debugger/DebugInfoWidget.cpp
     Debugger/Debugger.cpp
@@ -23,8 +22,6 @@ set(SOURCES
     Editor.cpp
     EditorWrapper.cpp
     FindInFilesWidget.cpp
-    FormEditorWidget.cpp
-    FormWidget.cpp
     Git/DiffViewer.cpp
     Git/GitFilesModel.cpp
     Git/GitFilesView.cpp
@@ -39,8 +36,6 @@ set(SOURCES
     ProjectFile.cpp
     ProjectTemplate.cpp
     TerminalWrapper.cpp
-    WidgetTool.cpp
-    WidgetTreeModel.cpp
     main.cpp
 )