remove unnecessary use of OUString constructor in XMLOFF module

Change-Id: I3bb704d2b1063cd8c2c903cbfa237a7723c321d2
remove unnecessary use of OUString constructor in XMLHELP module

Change-Id: I033bcf9cddc58f605fe8d65731f8b312410da7e5
remove unnecessary use of OUString constructor in WRITERFILTER module

Change-Id: Iba6fd6e2bb9b2a9e937149f3e3465b0817208a58
remove unnecessary use of OUString constructor in VCL module

Change-Id: Ie2b9aca5c3db46b43c53f72699fe828b28daeaa1