usp10: Remove a test that fails on Windows

[Jeff L]

This patch fixes a problem where a test fails in windows.  It may also 
fix a problem with 64 bit code but I am unable to test that.  I does 
this by declaring the HDC as global so it can be reused between test 
runs in test_ScriptItemIzeShapePlace and test_ScriptGetCMap.

Change log:
Fix glyph comparsion between tests.

Jeff