go.tools/go/ssa: remove windows test exclusion
go.tools/go/ssa: remove windows test exclusion

Issue 7189 was likely fixed with revision ed6ecfe1bc4e .

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://codereview.appspot.com/59230044

lattera/go.tools,karmakaze/go.tools,chenjianlong/go.tools,chenjianlong/go.tools,lattera/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,chenjianlong/go.tools,karmakaze/go.tools,lattera/go.tools