Remove QtViewer remnants

Per aothms's request on #8605: QtViewer is being superseded by the new
Bonsai Viewer, so its remains are deleted here (src/qtviewer, its
BUILD_QTVIEWER cmake option and add_subdirectory, and its references in
ci.yml's path filter, .gitignore, the conda recipe's license table, and
README's library table).

src/ifcopenshell-python/ifcopenshell/geom/app.py's qtViewer3d is
unrelated (pythonocc-core's own OCC.Display widget class, a name
coincidence) and is untouched.

Generated with the assistance of an AI coding tool.

cmake/CMakeLists.txt

@@ -79,7 +79,6 @@ option(BUILD_DOCUMENTATION "Build IfcOpenShell Documentation." OFF)
 option(BUILD_EXAMPLES "Build example applications." ON)
 option(BUILD_GEOMSERVER "Build IfcGeomServer executable (Open CASCADE is required)." ON)
 option(BUILD_IFCMAX "Build IfcMax, a 3ds Max plug-in, Windows-only." OFF)
-option(BUILD_QTVIEWER "Build IfcOpenShell Qt GUI Viewer" OFF) # QtViewer requires Qt6
 option(BUILD_IFCMODEL_UI "Build minimal Qt IFC model UI prototype" OFF)
 option(BUILD_BONSAIVIEWER "Build Bonsai Viewer" OFF) # Requires Qt6 + OpenGL 4.5
 option(BUILD_IFCOPENSHELL_PARSE_TESTS "Build C++ unit tests for IfcParse (fetches Catch2 v3)" OFF)
@@ -708,10 +707,6 @@ if(BUILD_IFCPYTHON)
     add_subdirectory(../src/ifcwrap ifcwrap)
 endif()
 
-if(BUILD_QTVIEWER)
-    add_subdirectory(../src/qtviewer qtviewer)
-endif()
-
 if(BUILD_IFCMODEL_UI)
     add_subdirectory(../src/ifcmodel-ui ifcmodel-ui)
 endif()