TComSlice: nits

--HG--
extra : amend_source : cb5f7ad8fa7f21d867e1d2af1ed7ed368d0af9b3
TComSlice: nits
primitive: remove dead ipfilter_p2s
primitive: remove dead ipfilter_s2p
primitive: remove dead pixelsub_ps
primitive: remove dead blockcpy_sp
primitive: nits