disable toolkit unit conversion test for now

There seems to be a bunch of problems:

On OSX the test crashes when no display can be found:
https://ci.libreoffice.org/job/lo_gerrit/25298/Config=macosx_clang_dbgutil/console

On windows the position seems to be wrong on some boxes, e.g.:
D:/lode/dev/core/toolkit/qa/cppunit/UnitConversion.cxx(149) : error : Assertion
Test name: `anonymous namespace'::ToolkitTest::testXUnitConversion
equality assertion failed
- Expected: 100
- Actual  : 72
- Window pos wrong

Change-Id: Id100817cf9024986f790c2bfbf2ddaefcd2dd080

toolkit/Module_toolkit.mk

@@ -23,9 +23,9 @@ $(eval $(call gb_Module_add_targets,toolkit,\
     Library_tk \
 ))
 
-$(eval $(call gb_Module_add_check_targets,toolkit,\
-    CppunitTest_toolkit \
-))
+#$(eval $(call gb_Module_add_check_targets,toolkit,\
+#    CppunitTest_toolkit \
+#))
 
 ifneq ($(OOO_JUNIT_JAR),)
 $(eval $(call gb_Module_add_subsequentcheck_targets,toolkit,\