writerfilter: remove unused WW8StructBase

Change-Id: I23c20ebf77666a64e3b65ce69ada1c1e1cfa5c21
writerfilter: remove unused WW8sprms.xsl

Change-Id: I82bd41c42ade8da50741af4fa66992d4ea95c463
writerfilter: remove unused WW8inc.xsl

Change-Id: Iba539b5546b5bf0dca9c9f19f2537cbcdd48becd