vcl: move Windows salgdi3.cxx to salfont.cxx - that's all it does!

Change-Id: I0a49bab5f410901d40c5b3b62a5a3f9d9946b8a0
Reviewed-on: https://gerrit.libreoffice.org/21057
Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>

vcl/Library_vcl.mk

@@ -698,7 +698,7 @@ $(eval $(call gb_Library_add_exception_objects,vcl,\
     vcl/win/gdi/salbmp \
     vcl/win/gdi/salgdi \
     vcl/win/gdi/salgdi2 \
-    vcl/win/gdi/salgdi3 \
+    vcl/win/gdi/salfont \
     vcl/win/gdi/salgdi_gdiplus \
     vcl/win/gdi/salnativewidgets-luna \
     vcl/win/gdi/salprn \