3rdparty/fx11-build: remove DX_SDK include dir, we get it from the en…

…vironment.

Fixes the build when using Qt 5.  Qt 5's qmake includes
an unquoted "C:\Program Files (x86)\[...]" in the Makefile,
causing the build to break.

3rdparty/fx11-build/fx11-build.pro

@@ -39,7 +39,6 @@ QMAKE_CXXFLAGS_RELEASE	*= -MT
 QMAKE_CXXFLAGS_DEBUG	*= -MTd
 
 INCLUDEPATH *= ../$$SOURCEDIR/inc ../$$SOURCEDIR/Binary
-INCLUDEPATH *= $(DXSDK_DIR)Include
 
 CONFIG(release, debug|release) {
   DEFINES *= NDEBUG