remove dead code, add missing RESTORE_XMM

vp8_filter_block1d16_h4_ssse3 was never called

because UNSHADOW_ARGS moves the stack by 'mov rsp, rbp', the issue was
masked. however, if/when win64 used those registers for persistant data,
issues could/will arise.

Change-Id: I56d6effca0aeba1f86082689771cb10145d39651