fix(build): Clean prior qt/dg_rc.py file before build

Since calls without pyqrcc5 may result in a broken file, clean prior
qt/gg_rc.py file before calling pyqrcc5.  This makes troubleshooting
pyqrcc5 issues more straightforward.

Fix #1103

build.py

@@ -129,6 +129,7 @@ def build_normal():
     print("Building localizations")
     build_localizations()
     print("Building Qt stuff")
+    Path("qt", "dg_rc.py").unlink(missing_ok=True)
     print_and_do("pyrcc5 {} > {}".format(Path("qt", "dg.qrc"), Path("qt", "dg_rc.py")))
     fix_qt_resource_file(Path("qt", "dg_rc.py"))
     build_help()